| 1. |
- Bjerregaard, Joachim, 1996, et al.
(author)
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Interpretation of H 2 -TPR from Cu-CHA Using First-Principles Calculations
- 2024
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In: Journal of Physical Chemistry C. - 1932-7447 .- 1932-7455. ; 128:11, s. 4525-4534
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Journal article (peer-reviewed)abstract
- Temperature-programmed reduction and oxidation are used to obtain information on the presence and abundance of different species in complex catalytic materials. The interpretation of the temperature-programmed reaction profiles is, however, often challenging. One example is H2 temperature-programmed reduction (H2-TPR) of Cu-chabazite (Cu-CHA), which is a material used for ammonia assisted selective catalytic reduction of NOx (NH3-SCR). The TPR profiles of Cu-CHA consist generally of three main peaks. A peak at 220 °C is commonly assigned to ZCuOH, whereas peaks at 360 and 500 °C generally are assigned to Z2Cu, where Z represents an Al site. Here, we analyze H2-TPR over Cu-CHA by density functional theory calculations, microkinetic modeling, and TPR measurements of samples pretreated to have a dominant Cu species. We find that H2 can react with Cu ions in oxidation state +2, whereas adsorption on Cu ions in +1 is endothermic. Kinetic modeling of the TPR profiles suggests that the 220 °C peak can be assigned to Z2CuOCu and ZCuOH, whereas the peaks at higher temperatures can be assigned to paired Z2Cu and Z2CuHOOHCu species (360 °C) or paired Z2Cu and Z2CuOOCu (500 °C). The results are in good agreement with the experiments and facilitate the interpretation of future TPR experiments.
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| 2. |
- Chaoquan, Hu, 1981, et al.
(author)
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Catalytic hydrogenation of C=C and C=O in unsaturated fatty acid methyl esters
- 2014
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In: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 4:8, s. 2427-2444
-
Research review (peer-reviewed)abstract
- Biodiesel derived from edible and non-edible oils has received much attention as a chemical feedstock or as a raw fuel alternative to the traditional diesel due to its renewability and biodegradability. However, the crude biodiesel containing large amounts of polyunsaturated fatty acid methyl esters (FAMEs) is susceptible to oxidation upon exposure to heat, light, and oxygen. Catalytic hydro-genation of biodiesel has been considered as a feasible and powerful technique to improve the oxidative stability of biodiesel and hence to provide stable raw materials for industrial applications. The catalytic hydrogenation of FAMEs is a complex process but basically consists of hydrogenation of C=C or C=O, depending on the desirable properties of final products. In this review, we summarize recent developments in hydrogenation of C=C and C=O in FAMEs with focus on catalysts, reaction mechanisms, and reactor conditions. The features of hydrogenation of FAMEs are generalized and the opportunities for future research in the field are outlined.
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| 3. |
- Chaoquan, Hu, 1981, et al.
(author)
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Methyl crotonate hydrogenation over Pt: Effects of support and metal dispersion
- 2016
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In: Applied Catalysis A: General. - : Elsevier BV. - 1873-3875 .- 0926-860X. ; 511, s. 106-116
-
Journal article (peer-reviewed)abstract
- Gas-phase hydrogenation of methyl crotonate (MC) has been studied over Pt supported on Al2O3, C, SiO2,and TiO2. The physicochemical properties of the catalysts were characterized by use of N2 physisorption,transmission electron microscopy and CO chemisorption. The effects of Pt dispersion and nature of the support on the catalytic properties of the catalysts were determined by measurements of the kinetic parameters for MC hydrogenation. The results clearly display MC inhibition effects on the hydrogenation over the catalysts. However, the degree of MC-inhibition is found to depend on both the Pt dispersion and the support used. For alumina a high Pt dispersion can promote the resistance of the catalyst against MC-inhibition, and even allow hydrogen adsorption to become equilibrated on the Pt surface. Compared to SiO2 and C supports, Al2O3 improves the resistance of the Pt surface against MC inhibition, whereas TiO2reduces the resistance. Possible reasons are suggested to understand the positive effect of Al2O3 on Pt against MC inhibition.
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| 4. |
- Chaoquan, Hu, 1981, et al.
(author)
-
Selectivity and kinetics of methyl crotonate hydrogenation over Pt/Al2O3
- 2015
-
In: Catalysis Science and Technology. - 2044-4753 .- 2044-4761. ; 5:3, s. 1716-1730
-
Journal article (peer-reviewed)abstract
- The hydrogenation of gas-phase methyl crotonate (MC) over Pt/Al2O3 was investigated with the aim to understand C=C hydrogenation in unsaturated methyl esters. Three Pt/Al2O3 catalysts with different Pt dispersions were prepared by varying calcination temperature and evaluated for MC hydrogenation. The main products were found to be methyl butyrate (MB) and methyl 3-butenoate (M3B), resulting from hydrogenation and shift of the C=C bond in MC, respectively. The measured activity for both hydrogenation and shift of the C=C in MC was found to depend on the Pt dispersion where higher Pt dispersion favors the C=C hydrogenation reaction. The effect of reactant concentrations on the activity and selectivity for MC hydrogenation over the Pt/Al2O3 catalyst was examined in detail. Under the investigated conditions, the C=C hydrogenation was found to have a negative reaction order with respect to MC concentration but a positive H2 order. Further understanding of the MC hydrogenation was provided from H2 chemisorption experiments over the catalyst with and without pre-adsorbed MC and from transient experiments using alternating MC and H2 feeds. Based on the present experimental results, a reaction pathway was proposed to describe gas-phase MC hydrogenation over Pt/Al2O3. In order to gain more insight into the reaction, a kinetic analysis of MC hydrogenation was performed by fitting a power-law model to the kinetic data, moreover, dissociative H2 adsorption on the catalyst was found to be the rate-determining step by comparing the power-law model with the overall rate expressions derived from mechanistic considerations.
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| 5. |
- Feng, Yingxin, 1994, et al.
(author)
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Simplified Kinetic Model for NH3‑SCR Over Cu‑CHA Based on First‑Principles Calculations
- 2023
-
In: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1572-9028 .- 1022-5528. ; 66:13-14, s. 743-749
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Journal article (peer-reviewed)abstract
- Selective catalytic reduction with ammonia as reducing agent (NH3-SCR) is an efficient technology to control NOx emission during oxygen excess. Catalysts based on Cu-chabazite (Cu-CHA) have shown good performance for NH3-SCR with high activity and selectivity at low temperature and good hydrothermal stability. Here, we explore a first-principles based kinetic model to analyze in detail which reaction steps that control the selectivity for N2 and the light-off temperature. Moreover, a simplified kinetic model is developed by fitting lumped kinetic parameters to the full model. The simplified model describes the reaction with high accuracy using only five reaction steps. The present work provides insight into the governing reaction mechanism and stimulates design of knowledge-based Cu-CHA catalysts for NH3-SCR.
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| 6. |
- Florén, Carl-Robert, 1988, et al.
(author)
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Modelling complete methane oxidation over palladium oxide in a porous catalyst using first-principles surface kinetics
- 2018
-
In: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 8:2, s. 508-520
-
Journal article (peer-reviewed)abstract
- A comprehensive model is developed for complete methane oxidation over supported palladium. The model is based on first-principles microkinetics and accounts for mass and heat transport in a porous catalytic layer. The turnover frequency (TOF) is simulated for wet exhaust gas compositions, exploring the effects of temperature and total pressure on the TOF. Three different temperature regimes are identified each with different dependency on the total pressure. The regimes originate from temperature and pressure dependent coverages of carbon dioxide and water, which are the most abundant surface species hindering methane dissociation at low temperatures. The TOF is controlled by surface kinetics below 400 °C whereas above 500 °C and up to 8 atm, internal mass transport is controlling. A combination of kinetics, external and internal mass transport controls the TOF at other reaction conditions. The physically meaningful model paves the way for extrapolation and optimization of catalyst design parameters for high catalytic efficiency.
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| 7. |
- Florén, Carl-Robert, 1988, et al.
(author)
-
Multiscale reactor modelling of total pressure effects on complete methane oxidation over Pd/Al2O3
- 2019
-
In: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 9:12, s. 3055-3065
-
Journal article (peer-reviewed)abstract
- A two-dimensional multiscale model is developed for complete methane oxidation in a continuous flow reactor. The model considers mass and heat transfer for a porous alumina supported palladium catalyst coated on a ceramic monolith substrate and the surface kinetics are described by a first-principles microkinetic model for complete methane oxidation over PdO(101). The temperature dependent conversion for a synthetic exhaust gas composition shows a delayed ignition but a higher conversion at elevated temperatures when the total pressure is increased from 1 to 10 atm. The simulations reveal a temperature and total pressure dependent operating point where the methane conversion is maximized. Analysis of the kinetics shows that the reaction is suppressed by bicarbonates, hydroxyl species and water originating from adsorbed carbon dioxide and water from the gas phase. The reaction order with respect to water and carbon dioxide at 1 atm is -0.94 and -0.99, respectively, and decreases with increasing total pressure. The developed model paves the way for exploring how design parameters and reaction conditions influence the complete methane oxidation reaction.
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| 8. |
- Han, Joonsoo, 1990, et al.
(author)
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Effect of SO 2 and SO 3 Exposure to Cu-CHA on Surface Nitrate and N 2 O Formation for NH 3 -SCR
- 2024
-
In: ACS ENGINEERING AU. - 2694-2488. ; In Press
-
Journal article (peer-reviewed)abstract
- We report effects of SO2 and SO3 exposure on ammonium nitrate (AN) and N2O formation in Cu-CHA used for NH3-SCR. First-principles calculations and several characterizations (ICP, BET, XRD, UV-vis-DRS) were applied to characterize the Cu-CHA material and speciation of sulfur species. The first-principles calculations demonstrate that the SO2 exposure results in both (bi)sulfite and (bi)sulfate whereas the SO3 exposure yields only (bi)sulfate. Furthermore, SOx adsorption on framework-bound dicopper species is shown to be favored with respect to adsorption onto framework-bound monocopper species. Temperature-programmed reduction with H-2 shows two clear reduction states and larger sulfur uptake for the SO3-exposed Cu-CHA compared to the SO2-exposed counterpart. Temperature-programmed desorption of formed ammonium nitrate (AN) highlights a significant decrease in nitrate storage due to sulfur species interacting with copper sites in the form of ammonium/copper (bi)bisulfite/sulfate. Especially, highly stable sulfur species from SO3 exposure influence the NO2-SCR chemistry by decreasing the N2O selectivity during NH3-SCR whereas an increased N2O selectivity was observed for the SO2-exposed Cu-CHA sample. This study provides fundamental insights into how SO2 and SO3 affect the N2O formation during ammonium nitrate decomposition in NH3-SCR applications, which is a very important topic for practical applications.
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| 9. |
- Heard, Christopher, 1988, et al.
(author)
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Kinetic Regimes in Ethylene Hydrogenation over Transition-Metal Surfaces
- 2016
-
In: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 6:5, s. 3277-3286
-
Journal article (peer-reviewed)abstract
- A first-principles microkinetic model has been developed and applied to ethylene hydrogenation over close-packed transition-metal surfaces of Ru, Rh, Pd, Os, Ir, and Pt. The model is based on density functional theory calculations, which have been used to determine the activation energies of the elementary steps of the reaction according to the Horuiti-Polanyi mechanism. A sensitivity analysis of the activity with respect to the kinetic parameters reveals distinctly different kinetic regimes across the periodic table. For Ru and Ir, the activity is controlled by the activation energy for ethylene to ethyl hydrogenation, whereas the other metals also have a sensitivity to the second hydrogenation step. The analysis shows, furthermore, that the activity could be enhanced considerably with minor reductions of the hydrogenation barriers.
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| 10. |
- Isapour Toutizad, Ghodsieh, 1986, et al.
(author)
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In situ DRIFT studies on N2O formation over Cu-functionalized zeolites during ammonia-SCR
- 2022
-
In: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 12:12, s. 3921-3936
-
Journal article (peer-reviewed)abstract
- The influence of the zeolite framework structure on the formation of N2O during ammonia-SCR of NOx was studied for three different copper-functionalized zeolite samples, namely Cu-SSZ-13 (CHA), Cu-ZSM-5 (MFI), and Cu-BEA (BEA). The evolution of surface species during the SCR reaction at different temperatures was monitored with step-response experiments using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) at different reaction conditions. Also, density functional theory (DFT) calculations were performed to assist the interpretation of the experimental results. The DRIFTS results indicate that NO+ and nitrate species are the main products formed during NO oxidation, and NO appears to adsorb on both Cu-Lewis and Al-Lewis acid sites. The DFT calculations for NO adsorption on the SSZ-13 sample reveal adsorption at Bronsted acid sites with similar adsorption energies but with a slight difference in NO+ stretching vibrations in the DRIFT spectra. Within the standard SCR reaction, in the O-H stretching region, the number of NH3 molecules adsorbed on the Bronsted acid sites is higher for the small-pore size sample compared to the medium- and large-pore zeolites. The obtained DRIFTS results for nitrate species are supported by DFT calculations by simulating the IR spectra of mobile and framework bound nitrate species, which both have a signature at 1604 cm(-1) associated with the O-N bond on NO3-. It is revealed that N2O is produced in a higher amount at lower temperatures for all three samples irrespective of the NO/NO2 ratio. Furthermore, the obtained results from both DRIFTS studies and flow reactor experiments show the higher formation of N2O for the large-pore zeolite compared to the medium- and small-pore zeolite.
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| 11. |
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| 12. |
- Achour, Abdenour, 1980, et al.
(author)
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Evaluation of kraft and hydrolysis lignin hydroconversion over unsupported NiMoS catalyst
- 2023
-
In: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947. ; 453
-
Journal article (peer-reviewed)abstract
- Catalytic hydroconversion of Kraft and hydrolysis lignins was for the first time compared in a batch reactor over an unsupported NiMoS-SBA catalyst. We also report the effect of key reaction parameters on the yields and properties of the products. The results obtained at 20 wt% catalyst loading for hydrolysis lignin showed the highest monomer yield of 76.0 wt%, which consisted of 39 wt% aromatics with the lowest alkylphenolics yield of 10.1 wt%. Identical operating conditions, 400 °C, 80 bar, 5 h at 10 wt% catalyst loading, were used to compare both lignins and the highest monomer yield (64.3 wt%) was found for the hydrolysis lignin, consisting of 16.0 wt% alkylphenolics and 20.1 wt% aromatic compounds. These values are considerably higher than those for Kraft lignin with its 47.0 wt% monomer yield. We suggest that the reason for high yields of monomeric units from hydrolysis lignin is that it is more reactive due to its lower ash and sulfur contents and the chemical structural differences compared to the Kraft lignin. More precisely, the bio-oil from hydrolysis lignin contained higher yields of small molecules, sourced from ring-opening of cellulose in the hydrolysis lignin, which could stabilize the reactive oligomeric groups. These yields were two to seven times higher from kraft and hydrolysis lignin, respectively, compared to those obtained without catalyst. The results showed that the NiMoS-SBA catalyst is a promising catalyst for reductive depolymerization of lignin and in addition that the regenerated catalyst had good stability for multiple reaction cycles.
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| 13. |
- Achour, Abdenour, 1980, et al.
(author)
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Towards stable nickel catalysts for selective hydrogenation of biomass-based BHMF into THFDM
- 2023
-
In: Journal of Environmental Chemical Engineering. - : Elsevier BV. - 2213-3437 .- 2213-2929. ; 11:2
-
Journal article (peer-reviewed)abstract
- Selective transformation of BHMF (2,5-bis(hydroxymethyl)furan) to THFDM (tetrahydrofuran-2,5-dimethanol) over a variety of structured Ni/Sx-Z1−x catalysts was investigated. The effects of support, Ni loading, solvent, temperature, pressure, and particle size on the conversion and selectivity were studied. Among them, the 10 wt% Ni catalyst supported on the SiO2:ZrO2 weight ratio of 90:10 (10NiS90Z10) exhibits the best performance in terms of BHMF conversion and THFDM selectivity. Its good performance was attributed to its well-balanced properties, that depend upon the ZrO2 content of the support in combination with SiO2, the active Ni sites-support interaction, and acidity/basicity ratio of each catalyst resulting in different Ni dispersions. Importantly, the 10NiS90Z10 catalyst showed a stable selectivity to THFDM (>94%), with 99.4% conversion of BHMF during 2 h reaction time. Poor catalytic activity resulted from excessive ZrO2 content (>10 wt%). The structural, textural, and acidity properties of NiSi100−y-Zry catalysts, tuned by selectively varying the Ni amount from 5 to 15 wt%, were critically investigated using numerous material characterization techniques. Catalyst recycling experiments revealed that the catalyst could be recycled several times without any measurable loss of catalytic activity.
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| 14. |
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| 15. |
- Arora, Prakhar, 1987, et al.
(author)
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Investigating the effect of Fe as a poison for catalytic HDO over sulfided NiMo alumina catalysts
- 2018
-
In: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 227, s. 240-251
-
Journal article (peer-reviewed)abstract
- The effect of iron (Fe) as poison present in renewable feeds was studied during hydrodeoxygenation (HDO) overmolybdenum based sulfided catalysts. The study was carried out at 6 MPa and 325 °C in batch reaction conditions. Different concentrations of Fe in the feed were tested over MoS2/Al2O3 and NiMoS/Al2O3. A notable drop in activity for the conversion of oxygenates was observed for both catalyst systems with an increased concentration of Fe in the feed. However, the changes in selectivity of products was opposite for unpromoted and Nipromoted catalysts. In the case of the NiMoS catalyst, at higher Fe concentration, the decarbonated product (C17 hydrocarbons) decreased while the direct hydrodeoxygenation product (C18 hydrocarbons)increased. On the contrary, for the base catalyst (MoS2), there was a decrease in the yield of direct hydrodeoxygenation (C18 hydrocarbons) products and an increase in yield of decarbonated products (C17 hydrocarbons). These sulfided catalysts have different sites for these two different reaction routes and they interacted differently with Fe during the deactivation process. With surface deposition of Fe, the ability of these catalysts to create active sites i.e. via sulfur vacancies deteriorated. TEM-EDX results suggested that the effect of Ni as a promoter for the decarbonation route was nullified and a resultant FeMo phase explains the drop in activity and change in selectivity.
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| 16. |
- Arora, Prakhar, 1987, et al.
(author)
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Kinetic study of hydrodeoxygenation of stearic acid as model compound for renewable oils
- 2019
-
In: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947. ; 364, s. 376-389
-
Journal article (peer-reviewed)abstract
- The kinetics during hydrodeoxygenation (HDO) of stearic acid (SA) was investigated to explore the fundamental chemistry and the reaction scheme involved for the reaction with a sulfide NiMo/Al2O3catalyst. Intermediates like octadecanal (C18 O) and octadecanol (C18 OH) were used to resolve the reaction scheme and explain the selectivity for the three major reaction routes (decarboxylation, decarbonylation and direct-HDO). Several reaction parameters, like temperature, pressure, feed concentration and batch-reactor stirring rate, were explored for their effect on changes in rate of conversion and selectivity. A weaker dependence on pressure (40–70 bar) and strong dependence on temperature (275–325 °C) was found for the product distribution during HDO of SA. A model based on Langmuir–Hinshelwood type kinetics was developed to correlate the experimental data. The model well predicted trends in variation of selectivities with the reaction conditions, in part by including intermediates like octadecanol and octadecanal and it predicted phenomenon like inhibiting effects of the fatty acid. The proposed kinetic model is expected to be applicable to liquid phase HDO of different renewable feeds containing long chain fatty acids, methyl esters and triglycerides etc.
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| 17. |
- Arora, Prakhar, 1987, et al.
(author)
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The role of catalyst poisons during hydrodeoxygenation of renewable oils
- 2021
-
In: Catalysis Today. - : Elsevier BV. - 0920-5861. ; 367, s. 28-42
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Journal article (peer-reviewed)abstract
- Hydrodeoxygenation (HDO) activity of NiMo catalysts have been evaluated in the presence of catalyst poisons in bio-based feedstocks. An in-house synthesized NiMo/Al2O3 catalyst was placed in a refinery unit for biofuel production. Iron (Fe), phosphorus (P) and metals were identified as major contaminants. Calcination treatment was explored to recover the activity of spent catalysts. The effect of Fe, K and phospholipid containing P and Na on catalyst deactivation during hydrodeoxygenation of stearic acid was simulated at lab-scale. Fe caused the most deactivation where the highest feed concentration of the Fe compound resulted in 1480 ppm Fe deposited on the catalyst. Elemental distribution along the radial axis of spent catalysts indicated: Fe deposited only to a depth of 100 μm irrespective of concentration while P and Na from phospholipid and K penetrated deeper in catalyst particles with a distribution profile that was found to be concentration dependent.
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| 18. |
- Azis, Muhammad Mufti, 1983, et al.
(author)
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Evaluation of H2 effect on NO oxidation over a diesel oxidation catalyst
- 2015
-
In: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 179, s. 542-550
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Journal article (peer-reviewed)abstract
- The influence of H2 on NO oxidation over Pt/Al2O3 as a model DOC catalyst was evaluated with various DOC feed mixtures. Discrimination of surface chemistry and exothermal effects due to addition of H2 was made based on differences in time scales of transient responses. H2 was proposed to retard Pt oxide formation mainly at low temperatures (ca.
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| 19. |
- Azis, Muhammad Mufti, 1983, et al.
(author)
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Kinetic modeling of C3H6 inhibition on NO Oxidation over Pt Catalyst
- 2016
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In: Bulletin of Chemical Reaction Engineering and Catalysis. - : Bulletin of Chemical Reaction Engineering and Catalysis. - 1978-2993. ; 11:1, s. 27-33
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Journal article (peer-reviewed)abstract
- Exhaust after treatment for lean burn and diesel engine is a complex catalytic system that consists of a number of catalytic units. Pt/Al2O3is often used as a model Diesel Oxidation Catalyst (DOC) that plays an important role to facilitate oxidation of NO to NO2. In the present study, we proposed a detailed kinetic model of NO oxidation as well as low temperature C3H6 inhibition to simulate temperatureprogrammed reaction (TPR) data for NO oxidation over Pt/Al2O3. A steady-state microkinetic model based on Langmuir-Hinshelwood mechanism for NO oxidation was proposed. In addition, low temperature C3H6inhibition was proposed as a result of site blocking as well as surface nitrite consumption. The model can explain the experimental data well over the studied temperature range.
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| 20. |
- Azis, Muhammad Mufti, 1983, et al.
(author)
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Kinetic modeling of H2-assisted C3H6 selective catalytic reduction of NO over silver alumina catalyst
- 2015
-
In: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947. ; 278, s. 394-406
-
Journal article (peer-reviewed)abstract
- A global kinetic model was developed for C3H6-SCR consisting of NO oxidation, C3H6 oxidation and C3H6-SCR reactions with and without H-2 over Ag-Al2O3. The model is based on a dual role of H-2 to remove inhibiting nitrates from the active sites as well as to modify/form new active Ag sites. For model development, a range of temperature programmed reaction (TPR) and transient feed experimental conditions were used. The proposed model was eventually also validated with additional transient experimental data. The kinetic model proposed in this study predicts the experimental data well for a wide-range of feed conditions. Evaluation of mass transfer resistance in the washcoat indicated that during H-2-assisted C3H6-SCR, mild internal mass transfer resistance for NO was predicted to be important already at 250 degrees C.
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| 21. |
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| 22. |
- Azis, Muhammad Mufti, 1983, et al.
(author)
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Microkinetic modeling of H2-assisted NO oxidation over Ag-Al2O3
- 2013
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In: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947. ; 221, s. 382-397
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Journal article (peer-reviewed)abstract
- A microkinetic model has been assembled to investigate the mechanism for NO oxidation over a monolith-supported Ag–Al2O3 catalyst both in the presence and absence of H2. The effect of H2 examined in the kinetic model was to reduce self inhibiting surface nitrate species on active silver sites. A reduced factorial design of inlet experimental conditions was used to generate transient experimental data. The kinetic model was developed based on a single channel reactor model which accounted for mass and heat transfer between gas and catalyst washcoat as well as mass transport resistance in the washcoat. In general, the modeling results could reproduce the transient experimental data well with correct levels of outlet concentrations and time scales for transient responses. It was found that the effect of increased NO and NO2 inlet concentration had a negative correlation with the NO oxidation conversion, which in the model was considered related to the formation of nitrate surface species. In addition, the model in agreement with experiments, clearly showed that H2 promoted the NO oxidation mainly at low temperature and this effect tended to decrease at elevated temperatures. When H2 was present in the feed, the kinetic model showed that H2 was consumed rapidly in the front part of the monolith. This was also seen in the experiments where in all cases H2 was entirely consumed. The rapid reaction of H2 along with resulting transport limitations indicated that the H2 promotion of the NO oxidation reaction may have been isolated to only a portion of the catalyst.
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| 23. |
- Azis, Muhammad Mufti, 1983, et al.
(author)
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On the role of H2 to modify surface NOx species over Ag-Al2O3 as lean NOx reduction catalyst: TPD and DRIFTS studies
- 2015
-
In: Catalysis Science and Technology. - 2044-4753 .- 2044-4761. ; 55:1, s. 296-309
-
Journal article (peer-reviewed)abstract
- Formation and stability of surface NOx species related to the promotional effect of H2 over Ag–Al2O3 as NOx reduction catalyst were investigated with temperature-programmed desorption and DRIFT spectroscopy. Formation of two groups of surface NOx species was found: a less thermally stable group of “low temperature (LT) species” and a more thermally stable group of “high temperature (HT) species”. The LT NOx was attributable to the decomposition of surface NOx species formed on the active sites where its elimination by addition of H2 or thermal decomposition correlated with higher NO oxidation and NOx reduction conversion. Under reaction conditions, these possibly inhibiting LT NOx species were stable up to about 300 °C and their formation depended on donation of oxygen from surface oxides. Removal of LT nitrate species by H2 accounted for only a fraction of the increased NO oxidation and NOx reduction conversion by co-feeding H2. Furthermore, it was also found that H2 facilitates formation of HT NOx that primarily corresponded to the decomposition of spectator species on the Al2O3 support identified as monodentate nitrate species. From TPD studies of C3H6-SCR, it was shown that H2 not only eliminated LT NOx but also promoted formation of greater quantities of adsorbed hydrocarbons.
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| 24. |
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| 25. |
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| 26. |
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| 27. |
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| 28. |
- Bergvall, Niklas, et al.
(author)
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Upgrading of fast pyrolysis bio-oils to renewable hydrocarbons using slurry- and fixed bed hydroprocessing
- 2024
-
In: Fuel processing technology. - : Elsevier B.V.. - 0378-3820 .- 1873-7188. ; 253
-
Journal article (peer-reviewed)abstract
- Liquefaction of lignocellulosic biomass through fast pyrolysis, to yield fast pyrolysis bio-oil (FPBO), is a technique that has been extensively researched in the quest for finding alternatives to fossil feedstocks to produce fuels, chemicals, etc. Properties such as high oxygen content, acidity, and poor storage stability greatly limit the direct use of this bio-oil. Furthermore, high coking tendencies make upgrading of the FPBO by hydrodeoxygenation in fixed-bed bed hydrotreaters challenging due to plugging and catalyst deactivation. This study investigates a novel two-step hydroprocessing concept; a continuous slurry-based process using a dispersed NiMo-catalyst, followed by a fixed bed process using a supported NiMo-catalyst. The oil product from the slurry-process, having a reduced oxygen content (15 wt%) compared to the FPBO and a comparatively low coking tendency (TGA residue of 1.4 wt%), was successfully processed in the downstream fixed bed process for 58 h without any noticeable decrease in catalyst activity, or increase in pressure drop. The overall process resulted in a 29 wt% yield of deoxygenated oil product (0.5 wt% oxygen) from FPBO with an overall carbon recovery of 68%.
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| 29. |
- Cheah, You Wayne, 1993, et al.
(author)
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Role of transition metals on MoS 2 -based supported catalysts for hydrodeoxygenation (HDO) of propylguaiacol
- 2021
-
In: Sustainable Energy and Fuels. - : Royal Society of Chemistry (RSC). - 2398-4902. ; 5:7, s. 2097-2113
-
Journal article (peer-reviewed)abstract
- Transition metal sulfides (TMSs) are typically used in the traditional petroleum refining industry for hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) applications. Bio-oils require an upgrading process like catalytic hydrodeoxygenation (HDO) to produce advanced biofuels and chemicals. Herein, MoS /γ-Al O promoted by transition metals like nickel (Ni), copper (Cu), zinc (Zn), and iron (Fe) was evaluated for the HDO of a bio-oil model compound, 4-propylguaiacol (PG) in a batch reactor at 340 °C under 50 bar H pressure. The catalyst screening results showed that the sulfided Ni-promoted catalyst gave a high 94% yield of deoxygenated cycloalkanes, however for the sulfided Cu-promoted catalyst, 42% of phenolics remain in the reaction medium after 5 h. The results also revealed that the sulfided Zn and Fe-promoted catalysts gave a final yield of 16% and 19% at full PG conversion, respectively, for deoxygenated aromatics. A kinetic model considering the main side reactions was developed to elucidate the reaction pathway of demethoxylation and dehydroxylation of PG. The developed kinetic model was able to describe the experimental results well with a coefficient of determination of 97% for the Ni-promoted catalyst system. The absence of intermediates like 4-propylcyclohexanone and 4-propylcyclohexanol during the reaction implies that direct deoxygenation (DDO) is the dominant pathway in the deoxygenation of PG employing sulfided catalysts. The current work also demonstrated that the activity of the transition metal promoters sulfides for HDO of PG could be correlated to the yield of deoxygenated products from the hydrotreatment of Kraft lignin. 2 2 3 2
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| 30. |
- Cheah, You Wayne, 1993, et al.
(author)
-
Slurry co-hydroprocessing of Kraft lignin and pyrolysis oil over unsupported NiMoS catalyst: A strategy for char suppression
- 2023
-
In: Chemical Engineering Journal. - 1385-8947. ; 475
-
Journal article (peer-reviewed)abstract
- Pyrolysis oil (PO) assisted Kraft lignin (KL) liquefaction over an unsupported NiMoS catalyst in a paraffin solvent was explored in this work. A paraffin solvent was used to represent hydrogenated vegetable oil (HVO) which is a biofuel. We have for the first time showed that when co-processing Kraft lignin with pyrolysis oil in a paraffin solvent the char formation could be completely suppressed. The complex composition of PO, containing various compounds with different functional groups, was able to aid the depolymerization pathways of lignin by obstructing the condensation path of reactive lignin derivatives. To further understand the role of different functional groups present in pyrolysis oil during lignin liquefaction, we investigate the co-hydroprocessing of Kraft lignin with various oxygenate monomers using unsupported NiMoS. 4-propylguaiacol (PG) was found to be the most efficient monomer for stabilizing the reactive lignin intermediates, resulting in a low char yield (3.7%), which was 4 times lower than the char production from Kraft lignin hydrotreatment alone. The suppressed rate of lignin fragment repolymerization can be attributed to the synergistic effect of functional groups like hydroxyl (-OH), methoxy (-OCH3), and propyl (-C3H7) groups present in PG. These groups were found to be able to stabilize the lignin depolymerized fragments and blocked the repolymerization routes enabling efficient lignin depolymerization. It was found that the presence of a co-reactant like PG during the heating period of the reactor acted as a blocking agent facilitating further depolymerization routes. Finally, a reaction network is proposed describing multiple routes of lignin hydroconversion to solid char, lignin-derived monomers, dimers, and oligomers, explaining why the co-processing of pyrolysis oil and Kraft lignin completely suppressed the solid char formation.
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| 31. |
- Cheah, You Wayne, 1993, et al.
(author)
-
Thermal annealing effects on hydrothermally synthesized unsupported MoS2 for enhanced deoxygenation of propylguaiacol and kraft lignin
- 2021
-
In: Sustainable Energy and Fuels. - 2398-4902. ; 5:20, s. 5270-5286
-
Journal article (peer-reviewed)abstract
- Catalytic hydrodeoxygenation (HDO) is an important hydrotreating process that is used to improve the quality of bio-oils to produce biomass-derived fuel components and chemicals. Molybdenum disulfide (MoS2) has been widely used as a catalyst in hydrodesulfurization (HDS) applications for several decades, which can be further improved for effective unsupported catalyst synthesis. Herein, we studied a universally applicable post-annealing treatment to a hydrothermally synthesized MoS2 catalyst towards developing efficient unsupported catalysts for deoxygenation. The effect of the annealing treatment on the catalyst was studied and evaluated for HDO of 4-propylguaiacol (PG) at 300 °C with 50 bar H2 pressure. The annealing of the as-synthesized catalyst under nitrogen flow at 400 °C for 2 h was found to enhance the HDO activity. This enhancement is largely induced by the changes in the microstructure of MoS2 after the annealing in terms of slab length, stacking degree, defect-rich sites and the MoS2 edge-to-corner site ratio. Besides, the effect of hydrothermal synthesis time and acid addition combined with the annealing treatment on the MoS2 catalytic activity was also studied for the same model reaction. The annealed MoS2 with a synthesis time of 12 h under an acidic environment was found to have improved crystallinity and exhibit the highest deoxygenation degree among all the studied catalysts. An acidic environment during the synthesis was found to be crucial in facilitating the growth of MoS2 micelles, resulting in smaller particles that affected the HDO activity. The annealed unsupported MoS2 with the best performance for PG hydrodeoxygenation was further evaluated for the hydrotreatment of kraft lignin and demonstrated a high deoxygenation ability. The results also indicate a catalyst with high activity for deoxygenation and hydrogenation reactions can suppress char formation and favor a high lignin bio-oil yield. This research uncovers the importance of a facile pretreatment on unsupported MoS2 for achieving highly active HDO catalysts.
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| 32. |
- Cheah, You Wayne, 1993, et al.
(author)
-
Upgrading of triglycerides, pyrolysis oil, and lignin over metal sulfide catalysts: A review on the reaction mechanism, kinetics, and catalyst deactivation
- 2023
-
In: Journal of Environmental Chemical Engineering. - : Elsevier BV. - 2213-3437 .- 2213-2929. ; 11:3
-
Research review (peer-reviewed)abstract
- Human activities such as burning fossil fuels for energy production have contributed to the rising global atmospheric CO2 concentration. The search for alternative renewable and sustainable energy sources to replace fossil fuels is crucial to meet the global energy demand. Bio-feedstocks are abundant, carbon-rich, and renewable bioresources that can be transformed into value-added chemicals, biofuels, and biomaterials. The conversion of solid biomass into liquid fuel and their further hydroprocessing over solid catalysts has gained vast interest in industry and academic research in the last few decades. Metal sulfide catalysts, a common type of catalyst being used in the hydroprocessing of fossil feedstocks, have gained great interest due to their low cost, industrial relevance, and easy implementation into the current refining infrastructures. In this review, we aim to provide a comprehensive overview that covers the hydrotreating of various bio-feedstocks like fatty acids, phenolic compounds, pyrolysis oil, and lignin feed using sulfided catalysts. The main objectives are to highlight the reaction mechanism/networks, types of sulfided catalysts, catalyst deactivation, and reaction kinetics involved in the hydrotreating of various viable renewable feedstocks to biofuels. The computational approaches to understand the application of metal sulfides in deoxygenation are also presented. The challenges and needs for future research related to the valorization of different bio-feedstocks into liquid fuels, employing sulfided catalysts, are also discussed in the current work.
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| 33. |
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| 34. |
- Creaser, Derek, 1966, et al.
(author)
-
Kinetic modeling of autothermal reforming of dimethyl ether
- 2010
-
In: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 49:20, s. 9712-9719
-
Journal article (peer-reviewed)abstract
- A global kinetic model was developed for the autothermal reforming of dimethyl ether (DME) over a Pd-Zn/Al2O3 catalyst on a cordierite monolith. A kinetic model consisting of five key overall reactions was found to capture the main features of experimental data. The modeling also accounted for heat transport effects in the reactor that are of importance when coupling the exothermic oxidation reactions with endothermic steam reforming reactions. The modeling confirmed that oxidation reactions dominate near the inlet of the reactor, generating a local hot spot. The heat from oxidation reactions accelerates the reforming reactions. Water adsorption was found to have a weak detrimental influence on the activity. Based on the model, the influence of the reactor scale and oxygen supply by air feed on the performance of the reactor was examined.
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| 35. |
- Creaser, Derek, 1966, et al.
(author)
-
Kinetic modeling of selective catalytic reduction of NOx with octane over Ag-Al2O3
- 2009
-
In: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 90:1-2, s. 18-28
-
Journal article (peer-reviewed)abstract
- A kinetic model for the selective catalytic reduction of NOx with octane over a Ag-Al2O3 catalyst was developed. Analysis of experimental data indicated that feed concentrations of NO and hydrogen had significant effects on the NOx conversion, indicating that nitrates poisoned the catalytic sites and hydrogen’s role was to reduce nitrate species. As a result nitrate poisoning was a key component of the kinetic model. Also in the model, gas phase n-octane reacted with surface oxygen to form surface hydrocarbon intermediate species that could either reduce surface NO2 species to nitrogen or be fully oxidized. An additional site was included in the model on which various oxidation reactions occurred when the NOx reduction site was fully poisoned by nitrate species. The model also accounted for experimentally observed large temperature increases due to hydrogen oxidation, during hydrogen feed. The model was constructed from transient experimental data, both with and without hydrogen feed and from a range of reactant concentrations and temperatures.
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| 36. |
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| 37. |
- Creaser, Derek, 1966, et al.
(author)
-
Modeling study of 5 kWe-scale autothermal diesel fuel reformer
- 2011
-
In: Applied Catalysis A: General. - : Elsevier BV. - 1873-3875 .- 0926-860X. ; 404, s. 129-140
-
Journal article (peer-reviewed)abstract
- A model was developed that successfully describes key operating features of a 5 kWe-scale autothermal diesel fuel reformer with an engineered monolith-supported Rh based catalyst. The model consisted of a kinetic model comprised of four overall reactions including total oxidation, fuel steam reforming, methane formation via fuel decomposition and the water–gas shift reaction. The model also accounted for heat and mass transport effects that were of importance when coupling the exothermic oxidation reactions with endothermic steam reforming reactions in a full-scale reformer. According to the model, the total oxidation and steam reforming reactions occurred simultaneously, however the heat effects of the oxidation reaction dominated near the reactor inlet resulting in a local hot spot. Transport resistances were found to hinder the rates of the main reactions, especially at higher temperature operating conditions. The model was primarily based on experimental data for a commercial low-sulphur diesel fuel (MK1), however it was found to also reasonably well describe the operation of the reactor with a diesel surrogate (n-tetradecane).
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| 38. |
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| 39. |
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| 40. |
- Di, Wei, 1986, et al.
(author)
-
CO2 hydrogenation to light olefins using In2O3 and SSZ-13 catalyst-Understanding the role of zeolite acidity in olefin production
- 2023
-
In: Journal of CO2 Utilization. - 2212-9820. ; 72
-
Journal article (peer-reviewed)abstract
- With the aim to explore the effect of acidic properties of zeolites in tandem catalysts on their performance for CO2 hydrogenation, two types of SSZ-13 zeolites with similar bulk composition, but different arrangements of framework Al, were prepared. Their morphology, pore structure, distribution of framework Al, surface acid strength and density, were explored. The results showed that SSZ-13 zeolites with isolated aluminum distribution could be successfully synthesized, however, they contained structural defects. During calcination, the framework underwent dealumination, resulting in weaker Brønsted acidity and lower crystallinity. The morphologies were, however, well preserved. Compared with the SSZ-13 zeolites, synthesized conventionally, these low acidity SSZ13 zeolites with isolated aluminum were good zeolite components in bifunctional catalysts for CO2 hydrogenation to light olefins. By combining with In2O3, they exhibited better catalytic performance for light olefin production during CO2 hydrogenation at low temperatures. Na+ cation exchange was used to adjust the Brønsted acid site (BAS) density with only minor changes to the cavity structure. Comparative experiments established that the BAS density of the zeolite, rather than the framework Al distribution (BAS distribution), overwhelmingly affected catalyst stability and product selectivity. A higher acid density reduced the selectivity for light olefins, while lower acid density tended to form inert coke species leading to rapid deactivation. The ideal amount of BAS density in the bifunctional catalyst was approximately 0.25 mmol/g, which exhibited 70% selectivity for light olefins among hydrocarbons, and 74% selectivity for CO without deactivation, after 12 h reaction at 325 celcius and 10 bar.
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| 41. |
- Di, Wei, 1986, et al.
(author)
-
Modulating the Formation of Coke to Improve the Production of Light Olefins from CO2 Hydrogenation over In2O3 and SSZ-13 Catalysts
- 2023
-
In: Energy & Fuels. - 1520-5029 .- 0887-0624. ; 37:22, s. 17382-17398
-
Journal article (peer-reviewed)abstract
- Moderately acidic aluminophosphates (SAPOs) are often integrated with methanol synthesis catalysts for the hydrogenation of CO2 to olefins, but they suffer from hydrothermal decomposition. Here, an alternative SSZ-13 zeolite with high hydrothermal stability is synthesized and coupled with an In2O3 catalyst in a hybrid system. Its performance regarding selectivity for olefins and coke formation was investigated for CO2 hydrogenation under varying temperatures and pressures. Various reactions occur, producing mainly CO and different hydrocarbons. The results indicate that the hydrogenation of hydrocarbons are dominant at high temperatures (around 400 °C) over SSZ-13 zeolite with a high acid density and that the coke deposition rate is slow. Polymethylbenzenes are the main coke species, but the selectivity for light olefins is low among hydrocarbons at high temperatures. However, at low temperatures (around 325 °C), and especially under high pressure (40 bar), methanol disproportionation becomes significant. This results in an increased selectivity for light olefins; however, it also leads to a rapid coke deposition, which gives inactive adamantanes as the main coke species that block the pores and cause rapid deactivation. However, after coking at 325 °C and regeneration at 400 °C under the reaction atmosphere, the accumulated adamantanes can be decomposed into smaller coke species, which reopens the channel structure and generates modulated active sites within the zeolite, resulting in a higher yield of olefins without deactivation. The performances of acidic SSZ-13 zeolites, with varying ratios of Si/Al in transient experiments, further verified that a dynamic balance exists between the formation and degradation of coke within the SSZ-13 zeolite during a long-term CO2 hydrogenation reaction. This balance can be achieved by optimizing the reaction conditions to match the acid density of the catalyst. Using the conditions of 20 bar and 375 °C, with a H2 to CO2 mole ratio of 3, the results obtained for the precoked hybrid catalysts of In2O3 and SSZ-13 (Si/Al = 25) exhibited very stable activity, with the selectivity for light olefins (based on hydrocarbons formed) of max. 70% after 100 h time-on-stream. This work provides new insights into the design of stable hybrid catalysts, especially the influence of a precoking process for SSZ-13 zeolite in the production of light olefins.
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| 42. |
- Feizie Ilmasani, Rojin, 1989, et al.
(author)
-
Deactivation of phosphorus-poisoned Pd/SSZ-13 for the passive adsorption of NOx
- 2022
-
In: Journal of Environmental Chemical Engineering. - : Elsevier BV. - 2213-3437 .- 2213-2929. ; 10:3
-
Journal article (peer-reviewed)abstract
- Automotive catalysts can be exposed to various poisonous substances that can cause physical or chemical deactivation. One of such poisons is phosphorous, which originates from lubricant oils. This study focuses on the phosphorus deactivation of Pd/SSZ-13 used as a passive NOx adsorber (PNA). A clear deactivation caused by phosphorus was observed, and it was increased by increasing the content of phosphorous. It was concluded that phosphorous can cause both physical and chemical deactivation. This was evident from XPS analysis, where the presence of phosphorus pentoxide (P2O5) causes physical deactivation whereas metaphosphate (PO3-) and phosphate (PO43-) cause chemical deactivation. Also, it was shown that metaphosphates (PO3-) become the dominant phosphorous species at higher P concentrations. Lesser amounts of O2 were released in P-poisoned Pd/SSZ-13, as was found in oxygen TPD when increasing the P concentration, due to the presence of more PO3- species. Furthermore, XRD and 27Al NMR analyses revealed that phosphorus also interacted with alumina in the zeolite framework by forming Al-O-P species; this was also supported by SEM-EDX, where there was a clear overlap of P with Al and Pd spectra. DRIFTS analysis showed that OH groups in contact with the zeolite structure became contaminated by phosphorus and caused a chemical deactivation of Pd/SSZ-13. It was also found that, during multiple cycles, the PNA capacity decreased for phosphorus-poisoned samples. This was caused by the transformation of P2O5, which causes physical blocking, to PO3-, which interacts chemically with the palladium species.
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| 43. |
- Feizie Ilmasani, Rojin, 1989, et al.
(author)
-
Influencing the NOx Stability by Metal Oxide Addition to Pd/BEA for Passive NOx Adsorbers
- 2020
-
In: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 59:21, s. 9830-9840
-
Journal article (peer-reviewed)abstract
- Passive NOx adsorption performance was investigated for Pd-based BEA zeolite as a reference sample along with ceria, zirconium, and lanthanum as different promoters. The La-promoted sample showed favorable NOx desorption behavior regarding greater quantities of NOx release at temperatures higher than 200 degrees C. The study was therefore mainly focused on the La-promoted sample and Pd/BEA, since the largest effect was seen using La as a promoter. The effect of water and hydrogen pretreatments for passive NOx adsorption (PNA) processes was therefore studied for La-Pd/BEA and compared with that for pure Pd/BEA. It was shown that the presence of water reduces the NOx desorption at lower temperature. Hydrogen pretreatment decreases the NOx uptake and shifts the adsorption and desorption temperatures to higher values. Interestingly, the La-Pd/BEA sample was less sensitive to H-2 pretreatment. Temperature-programmed oxidation (TPO) and X-ray photoelectron spectroscopy (XPS) results indicated the presence of more stable Pd oxide sites for La-Pd/BEA. Furthermore, Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis suggested that NO is adsorbed with stronger and more stable bonds in the form of nitrates compared with the Pd/BEA reference sample.
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| 44. |
- Feizie Ilmasani, Rojin, 1989, et al.
(author)
-
Investigation of CO Deactivation of Passive NOx Adsorption on La Promoted Pd/BEA
- 2022
-
In: Emission Control Science and Technology. - : Springer Science and Business Media LLC. - 2199-3629 .- 2199-3637. ; 8:1-2, s. 63-77
-
Journal article (peer-reviewed)abstract
- Passive NOx adsorption (PNA) is a method, in which NOx can be stored at low temperatures and released at higher temperatures where the urea decomposition is functional during selective catalytic reduction (i.e., above 180–200 °C). We have studied the promotion of Pd/BEA with La as a PNA in the presence of high CO concentration. Both the reference and promoted samples exhibited a significant loss of NOx adsorption/desorption capacity after multiple cycles using 4000 ppm CO. However, already after 5 cycles, 99% of the NOx released between 200 and 400 °C was lost for Pd/BEA, compared to only 64% for Pd-La/BEA, which thereafter was stable. XPS and O2-TPD clearly showed that the Pd species were influenced by La. The PNA deactivation in the presence of CO could be related to Pd reduction followed by migration and the formation of more PdOx clusters, as observed by O2-TPD analysis. Interestingly, significantly more PdOx clusters formed on Pd/BEA after 10 cycles compared to Pd-La/BEA.
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| 45. |
- Florén, Carl-Robert, 1988, et al.
(author)
-
Total oxidation of methane over Pd/Al2O3at pressures from 1 to 10 atm
- 2020
-
In: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 10:16, s. 5480-5486
-
Journal article (peer-reviewed)abstract
- The kinetics of total methane oxidation over a 0.15 wt% Pd/Al2O3 monolith catalyst has been measured during temperature programmed methane oxidation experiments at total pressures from 1 to 10 atm and compared with multiscale simulations. The methane conversion can be significantly enhanced by increasing the total pressure at temperatures above 350 °C, which is thanks to a longer residence time that dominates over decreased bulk gas diffusion rates and product inhibition. For the present catalyst, the external mass transfer impacts the methane conversion above 4 atm. With increasing total pressure, the observed methane reactions order decreases at 350 °C whereas it increases at 450 °C due to a more pronounced product inhibition at the lower temperatures. This is also reflected in the apparent activation energy, which increases with increasing total pressure. The multiscale simulations capture the general trends of the experimental results but overestimate the methane conversion at higher temperatures and total pressures. The overestimated activity indicates of an overestimated number of active sites and/or an underestimated external mass transfer resistance.
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| 46. |
- Funkenbusch, Li Lu T., et al.
(author)
-
Catalytic hydrotreatment of pyrolysis oil phenolic compounds over Pt/Al2O3 and Pd/C
- 2019
-
In: Fuel. - : Elsevier BV. - 0016-2361. ; 243, s. 441-448
-
Journal article (peer-reviewed)abstract
- A batch catalytic slurry reactor system was used to study the hydrodeoxygenation (HDO) of pyrolysis oil model compounds at high conversions and conditions similar to petroleum hydrotreatment reactors. The lignin fraction of pyrolysis oil was represented in this study by anisole, m-cresol and phenol, both individually and blended in pairs. Experiments were run from 250 °C to 350 °C using platinum on alumina (Pt/Al2O3) or palladium on carbon (Pd/C) in a Parr reactor at 50 bar. The Pt/Al2O3 catalysts exhibited ring saturation, demethylation and hydrodeoxygenation, with temperature-dependent pathway shifts. Tests with blended pairs yielded no secondary reactions but competitive adsorption for catalyst active sites was observed. Tests with Pd/C showed ring saturation followed by methanol abstraction. Rate constants and adsorption parameters were fitted to a Langmuir-Hinshelwood model for each catalyst and compound. Arrhenius relationships for those rate constants and surface adsorption parameters were then calculated. When used in a slurry reactor model with catalyst-specific reaction data, the product composition, hydrogen consumption, and energy requirements are well predicted for a known feed and set of reactor conditions.
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| 47. |
- Ghosh, Sreetama, 1990, et al.
(author)
-
Experimental and kinetic modeling studies of methanol synthesis from CO 2 hydrogenation using In 2 O 3 catalyst
- 2021
-
In: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947. ; 416
-
Journal article (peer-reviewed)abstract
- Catalytic hydrogenation of CO2 to methanol has gained considerable interest for its significant role in CO2 utilization using heterogeneous catalysts. This study is the first to propose a kinetic model based on Langmuir-Hinshelwood-Hougen-Watson (LHHW) mechanism for CO2 hydrogenation to methanol over a highly effective indium oxide (In2O3) catalyst. The work focuses on different reaction conditions mainly revolving around the variation of operating temperature, total reactor pressure, H2/CO2 molar feed ratio and weight hourly space velocity (WHSV) of the system. The experimental data were modeled using a competitive single-site kinetic model based on LHHW rate equations. A parameter optimization procedure was undertaken to determine the kinetic parameters of the developed rate equations. The model predicts that when the methanol synthesis reaction becomes equilibrium limited, the progress of the RWGS reaction forces the methanol yield to decrease due to the reversal of the methanol synthesis reaction. A mixture of CO2 and H2 has been used as the reactor feed in all the cases. Significantly w.r.t. the CO2 partial pressure, the reaction rate for methanol synthesis initially increased and then slightly decreased indicating a varying order. The single-site model accurately predicted the trends in the experimental data which would enable the development of reliable reactor and process designs.
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| 48. |
- Ghosh, Sreetama, 1990, et al.
(author)
-
Methanol mediated direct CO 2 hydrogenation to hydrocarbons: Experimental and kinetic modeling study
- 2022
-
In: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947. ; 435
-
Journal article (peer-reviewed)abstract
- Carbon dioxide can be utilized as a feedstock to produce chemicals and renewable fuels sustainably. CO2 hydrogenation to hydrocarbons through a methanol mediated pathway requires a more detailed study, examining interactions between reaction processes leading to different product selectivities. In this particular work, we propose a kinetic model for the direct CO2 hydrogenation to different hydrocarbon products over an In2O3/HZSM-5 bifunctional catalytic bed. The model includes a CO2 hydrogenation to methanol model based on a Langmuir Hinshelwood Hougen Watson (LHHW) reaction mechanism over In2O3 catalyst combined with a lump-type methanol to hydrocarbon (MTH) model over the HZSM-5 zeolite. Interestingly, the combined model could largely predict the suppression of the reverse water gas shift (RWGS) reaction and an increase in the yield of hydrocarbons compared to the formation of methanol in case of the same reaction conditions carried out with only the methanol synthesis catalyst (In2O3). Further, by varying the mass ratio of the individual components of the bifunctional catalytic bed, it was demonstrated that a higher outlet concentration of methanol achieved with a higher mass ratio of the methanol synthesis catalyst caused less suppression of the RWGS reaction and shifted the hydrocarbon product distribution to a slightly larger share of higher hydrocarbons. These changes in product selectivity caused by variation of the catalyst mass ratio were both also successfully reproduced by the model. Therefore, a comparison between the experimental results and the model predictions shows that this model, including equilibrium effects for the reactions, can accurately predict the trends of the experimental findings for direct CO2 hydrogenation to hydrocarbons over the In2O3/HZSM-5 catalyst.
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| 49. |
- Han, Joonsoo, 1990, et al.
(author)
-
N 2 O Formation during NH 3 -SCR over Different Zeolite Frameworks: Effect of Framework Structure, Copper Species, and Water
- 2021
-
In: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 60:49, s. 17826-17839
-
Journal article (peer-reviewed)abstract
- The formation characteristics of N2O were investigated with respect to copper-functionalized zeolites, i.e., Cu/SSZ-13 (CHA), Cu/ZSM-5 (MFI), and Cu/BEA (BEA) and compared with the corresponding zeolites in the H form as references to elucidate the effect of the framework structure, copper addition, and water. Temperature-programmed reduction with hydrogen showed that the CHA framework has a higher concentration of Cu2+ (Z2Cu) compared to MFI and BEA. The characterizations and catalyst activity results highlight that CHA has a framework structure that favors high formation of ammonium nitrate (AN) in comparison with MFI and BEA. Moreover, AN formation and decomposition were found to be promoted in the presence of Cu species. On the contrary, lower N2O formation was observed from Cu/CHA during standard and fast SCR reactions, which is proposed to be due to highly stabilized AN inside the zeolite cages. On the other hand, significant amounts of N2O were released during heating due to decomposition of AN, implying pros and cons of AN stability for Cu/CHA with possible uncontrolled N2O formation during transient conditions. Additionally, important effects of water were found, where water hinders AN formation and increases the selectivity for decomposition to NO2 instead of N2O. Thus, less available AN forming N2O was observed in the presence of water. This was also observed in fast SCR conditions where all Cu/zeolites exhibited lower continuous N2O formation in the presence of water.
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| 50. |
- Ho, Hoang Phuoc, 1983, et al.
(author)
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Effect of the Preparation Methods on the Physicochemical Properties of Indium-Based Catalysts and Their Catalytic Performance for CO 2 Hydrogenation to Methanol
- 2024
-
In: Energy & Fuels. - 1520-5029 .- 0887-0624. ; 38:6, s. 5407-5420
-
Journal article (peer-reviewed)abstract
- Indium oxides (In2O3) and indium oxides supported zirconia (ZrO2) have been known possible alternatives for conventional copper-based catalysts in the CO2-hydrogenation to methanol. This study aims to investigate the effect of preparation techniques on the physicochemical properties of indium-based materials and their catalytic performance for the hydrogenation of CO2 to methanol. Two series of both single oxide In2O3 and binary In2O3-ZrO2 have been synthesized by combustion, urea hydrolysis, and precipitation with different precipitating agents (sodium carbonate and ammonia/ethanol solution). Physicochemical properties of materials are characterized by elemental analysis, XRD, N2 physisorption, SEM/EDX, micro-Raman, XPS, H2-TPR, and CO2-TPD. Cubic In2O3 was the common phase generated by all four synthesis methods, except for urea hydrolysis, where rhombohedral In2O3 was additionally present. The combustion method produced the materials with the lowest specific surface areas while the precipitation using ammonia/ethanol aided in creating more oxygen defects. The synthesis methods strongly influenced the degree of interaction between the oxides and resulted in improvements in properties that boosted the catalytic performance of the binary oxides compared to their single-oxide counterparts.
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