| 1. |
- Atakan, Aylin, et al.
(författare)
-
Impact of the morphological and chemical properties of copper-zirconium-SBA-15 catalysts on the conversion and selectivity in carbon dioxide hydrogenation
- 2019
-
Ingår i: Journal of Colloid and Interface Science. - : ACADEMIC PRESS INC ELSEVIER SCIENCE. - 0021-9797 .- 1095-7103. ; 546, s. 163-173
-
Tidskriftsartikel (refereegranskat)abstract
- A hybrid catalyst consisting of Zr-doped mesoporous silica (Zr-SBA-15) supports with intergrown Cu nanoparticles was used to study the effects of a catalysts chemical states on CO2 hydrogenation. The chemical state of the catalyst was altered by using tetraethyl orthosilicate (TEOS) or sodium metasilicate (SMS) as the silica precursor in the synthesis of the Zr-SBA-15 framework, and infiltration (Inf) or evaporation induced wetness impregnation (EIWI) as the Cu loading method. As a result, the silica precursor mainly affects the activity of the catalyst whereas the Cu loading method alters the selectivity of the products. TEOS materials exhibit a higher catalytic activity compared to SMS materials due to different Zr dispersion and bonding to the silica matrix. EIWI catalysts display selectivity for methanol formation, while the Inf ones enable methanol conversion to DME. This is correlated to a higher Zr content and lower Cu oxidation states of EIWI prepared catalysts. (C) 2019 Elsevier Inc. All rights reserved.
|
|
| 2. |
- Atakan, Aylin, et al.
(författare)
-
Synthesis of a Cu-infiltrated Zr-doped SBA-15 catalyst for CO2 hydrogenation into methanol and dimethyl ethert
- 2017
-
Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : ROYAL SOC CHEMISTRY. - 1463-9076 .- 1463-9084. ; 19:29, s. 19139-19149
-
Tidskriftsartikel (refereegranskat)abstract
- A catalytically active nanoassembly comprising Cu-nanoparticles grown on integrated and active supports (large pore Zr-doped mesoporous SBA-15 silica) has been synthesized and used to promote CO2 hydrogenation. The doped mesoporous material was synthesized using a sal-gel method, in which the pore size was tuned between 11 and 15 nm while maintaining a specific surface area of about 700 m(2) g (1). The subsequent Cu nanoparticle growth was achieved by an infiltration process involving attachment of different functional groups on the external and internal surfaces of the mesoporous structure such that 7-10 nm sized Cu nanoparticles grew preferentially inside the pores. Chemisorption showed improved absorption of both CO2 and H-2 for the assembly compared to pure SBA-15 and 15% of the total CO2 was converted to methanol and dimethyl ether at 250 degrees C and 33 bar.
|
|
| 3. |
- Atakan, Aylin, et al.
(författare)
-
Time evolution of the CO2 hydrogenation to fuels over Cu-Zr-SBA-15 catalysts
- 2018
-
Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 362, s. 55-64
-
Tidskriftsartikel (refereegranskat)abstract
- Time evolution of catalytic CO2 hydrogenation to methanol and dimethyl ether (DME) has been investigated in a high-temperature high-pressure reaction chamber where products accumulate over time. The employed catalysts are based on a nano-assembly composed of Cu nanoparticles infiltrated into a Zr doped SiOx mesoporous framework (SBA-15): Cu-Zr-SBA-15. The CO2 conversion was recorded as a function of time by gas chromatography-mass spectrometry (GC-MS) and the molecular activity on the catalyst’s surface was examined by diffuse reflectance in-situ Fourier transform infrared spectroscopy (DRIFTS). The experimental results showed that after 14 days a CO2 conversion of 25% to methanol and DME was reached when a DME selective catalyst was used which was also illustrated by thermodynamic equilibrium calculations. With higher Zr content in the catalyst, greater selectivity for methanol and a total 9.5% conversion to methanol and DME was observed, yielding also CO as an additional product. The time evolution profiles indicated that DME is formed directly from methoxy groups in this reaction system. Both DME and methanol selective systems show the thermodynamically highest possible conversion.
|
|
| 4. |
- Björk, Emma, et al.
(författare)
-
Formation of block-copolymer-templated mesoporous silica
- 2018
-
Ingår i: Journal of Colloid and Interface Science. - : ACADEMIC PRESS INC ELSEVIER SCIENCE. - 0021-9797 .- 1095-7103. ; 521, s. 183-189
-
Tidskriftsartikel (refereegranskat)abstract
- In situ attenuated total reflectance Fourier transform infrared spectroscopy is used to monitor the chemical evolution of the mesoporous silica SBA-15 from hydrolysis of the silica precursor to final silica condensation after the particle formation. Two silica precursors, tetraethyl orthosilicate (TEOS) or sodium metasilicate (SMS) were used, and the effects of additive (heptane and NH4F) concentrations were studied. Five formation stages are identified when TEOS is used as the precursor. The fourth stage correlates with the appearance and evolution of diffraction peaks recorded using in situ small angle X-ray diffraction. Details of the formed silica matrix are observed, e.g. the ratio between six-fold cyclic silica rings and linear bonding increases with the NH4F concentration. The TEOS hydrolysis time is independent of the NH4F concentration for small amounts of heptane, but is affected by the size of the emulsion droplets when the heptane amount increases. Polymerization and condensation rates of both silica precursors are affected by the salt concentration. Materials synthesized using SMS form significantly faster compared to TEOS-materials due to the pre-hydrolysis of the precursor. The study provides detailed insights into how the composition of the synthesis solution affects the chemical evolution and micellar aggregation during formation of mesoporous silica. (C) 2018 Elsevier Inc. All rights reserved.
|
|
| 5. |
- Jiao, Fei, et al.
(författare)
-
Nanofibrillated Cellulose-Based Electrolyte and Electrode for Paper-Based Supercapacitors
- 2018
-
Ingår i: ADVANCED SUSTAINABLE SYSTEMS. - : Wiley. - 2366-7486. ; 2:1
-
Tidskriftsartikel (refereegranskat)abstract
- Solar photovoltaic technologies could fully deploy and impact the energy conversion systems in our society if mass-produced energy-storage solutions exist. A supercapacitor can regulate the fluctuations on the electrical grid on short time scales. Their mass-implementation requires the use of abundant materials, biological and organic synthetic materials are attractive because of atomic element abundancy and low-temperature synthetic processes. Nanofibrillated cellulose (NFC) coming from the forest industry is exploited as a three-dimensional template to control the transport of ions in an electrolyte-separator, with nanochannels filled of aqueous electrolyte. The nanochannels are defined by voids in the nanocomposite made of NFC and the proton transporting polymer polystyrene sulfonic acid PSSH. The ionic conductivity of NFC-PSSH composites (0.2 S cm(-1) at 100% relative humidity) exceeds sea water in a material that is solid, feel dry to the finger, but filled of nanodomains of water. A paper-based supercapacitor made of NFC-PSSH electrolyte-separator sandwiched between two paper-based electrodes is demonstrated. Although modest specific capacitance (81.3 F g(-1)), power density (2040 W kg(-1)) and energy density (1016 Wh kg(-1)), this is the first conceptual demonstration of a supercapacitor based on cellulose in each part of the device; which motivates the search for using paper manufacturing as mass-production of energy-storage devices.
|
|
| 6. |
- Kalered, Emil, et al.
(författare)
-
Infrared Fingerprints of the CO2 Conversion into Methanol at Cu(s)/ZrO2(s): An Experimental and Theoretical Study
- 2023
-
Ingår i: ChemCatChem. - : WILEY-V C H VERLAG GMBH. - 1867-3880 .- 1867-3899.
-
Tidskriftsartikel (refereegranskat)abstract
- The methanol economy is an attractive approach to tackle the current concerns over the depletion of natural resources and the global warming intrinsically associated with the use of fossil fuels. This can be achieved by hydrogenation of carbon dioxide to produce methanol, a liquid fuel with potential use in civil transportation. In this study, we aim to pinpoint the intermediates that are involved in the catalytic CO2 conversion into methanol on pure zirconia (ZrO2), Cu and Cu/ZrO2 systems. To accomplish this, we make use of infrared (IR) spectroscopy measurements and quantum chemical simulations within the hybrid density functional theory (DFT) framework. At 250 degrees C and p similar to 30 bar, the main species formed on the partially hydroxylated ZrO2 is bidentate formate, whereas the co-production of bicarbonate is relevant upon cooling to T=25 degrees C. On pure Cu, the IR fingerprints of methanol and carbon dioxide indicate their presence in the gas phase and surface environment, albeit formate/formic acid and methoxy species are also detected at these experimental conditions. The production of methanol on Cu/ZrO2 is mostly dependent on the Cu catalyst, but the higher amount of the methoxy intermediate can be correlated with the consumption of formate adsorbed on ZrO2 or at the Cu/ZrO2 interface. On the Cu/ZrO2 mixture, the reaction mechanism is likely to involve formate as the main intermediate, instead of CO which would result from the reverse water-gas shift reaction. Ultimately, the higher activity shown by the Cu/ZrO2 mixture might be associated with the extra-production of methoxy/methanol catalyzed by ZrO2 in the presence of Cu.
|
|
| 7. |
- Mäkie, Peter, et al.
(författare)
-
Adsorption of trimethyl phosphate and triethyl phosphate on dry and water pre-covered hematite, maghemite, and goethite nanoparticles
- 2013
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier. - 0021-9797 .- 1095-7103. ; 392, s. 349-358
-
Tidskriftsartikel (refereegranskat)abstract
- Adsorption of trimethyl phosphate (TMP) and triethyl phosphate (TEP) on well-characterized nanoparticles of hematite (α-Fe(2)O(3)), maghemite (γ-Fe(2)O(3)), and goethite (α-FeOOH) has been studied by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), 2D correlation DRIFTS analysis, and X-ray photoelectron spectroscopy (XPS) on dry and water pre-covered surfaces. It is shown that, at room temperature and low coverage, both TMP and TEP coordinate to Lewis acid Fe sites through the O phosphoryl atom on hematite and maghemite, while hydrogen bonding to Brønstedt acid surface OH groups dominates on goethite. At room temperature, slow dissociation of TMP occurs on the iron (hydr)oxide nanoparticles, whereby a methoxy group is displaced to form surface methoxy, leaving adsorbed dimethyl phosphate (DMP). Methoxy is further decomposed to formate, suggesting an oxidative degradation pathway in synthetic air on the oxide particles. Relatively, larger amounts of DMP and surface methoxy form on maghemite, while more formate is produced on hematite. Upon TMP adsorption on dry goethite nanoparticles, no oxidation surface products were detected. Instead, a slow TMP hydrolysis pathway is observed, yielding orthophosphate. It is found that pre-adsorbed water stimulates the hydrolysis of TMP. In contrast to TMP, TEP adsorbs molecularly on all iron hydr(oxide) nanoparticles. This is attributed to the longer aliphatic chain, which stabilizes the loss of charge on the methoxy CO bonds by charge redistribution upon phosphoryl O coordination to Fe surface atoms. The presented results implicate different reactivity depending on specific molecular structure of the organophosphorus compound (larger functional groups can compensate loss of charge due to surface coordination) and iron (hydr)oxide surface structure (exposing Lewis acid or Brønstedt acid sites).
|
|
| 8. |
- Mäkie, Peter, et al.
(författare)
-
Adsorption of Trimethyl Phosphate on Maghemite, Hematite and Goethite Nanoparticles
- 2011
-
Ingår i: Journal of Physical Chemistry A. - : American Chemical Society. - 1089-5639 .- 1520-5215. ; 115:32, s. 8948-8959
-
Tidskriftsartikel (refereegranskat)abstract
- Adsorption of trimethyl phosphate (TMP) on well-characterized hematite, maghemite and goethite nanoparticles was studied by in situ DRIFT spectroscopy as a model system for adsorption of organophosphorous (OP) compounds on iron minerals. The iron minerals were characterized by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), specific surface area and pore size distribution. The minerals were found to consist of stoichimetrically and morphologically well-defined maghemite, hematite and goethite nanoparticles. Analysis of in situ diffuse reflectance Fourier transform (DRIFT) spectroscopy show that TMP bonds mainly to Lewis acid Fe sites through the O phosphoryl atom (-P=O-Fe) on hematite and maghemite. On goethite most TMP molecules bond to Brønstedt acid surface OH groups and form hydrogen bonded surface complexes. The vibrational mode analysis and uptake kinetics suggest two main reasons for the observed trend of reactivity towards TMP (hematite > maghemite > goethite): (i) Larger number of accessible Lewis acid adsorption sites on hematite, (ii) stronger interaction between the Lewis acid Fe sites and the phosphoryl O atom on TMP for hematite and maghemite compared to goethite with concomitant formation of surface coordinated TMP and dimethyl phosphate intermediates. As a result, on the oxides a surface oxidation pathways dominates during the initial adsorption, which results in the formation of surface methoxy and formate. In contrast, on goethite a slower hydrolysis pathway is identified which eventually yields phosphoric acid. The observed trends of the reactivity and analysis of the corresponding surface structure and particle morphology suggest an intimate relation between the surface chemistry of exposed crystal facets on the iron minerals. These results are important to understand OP surface chemistry on iron minerals.
|
|
| 9. |
- Mäkie, Peter, et al.
(författare)
-
Solar Light Degradation of Trimethyl Phosphate and Triethyl Phosphate on Dry and Water-Precovered Hematite and Goethite Nanoparticles
- 2012
-
Ingår i: The Journal of Physical Chemistry C. - Washtington : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 116:28, s. 14917-14929
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the solar-light-mediated degradation of trimethyl phosphate (TMP) and triethyl phosphate (TEP) on hematite and goethite nanoparticles in synthetic air. Adsorption and photoreactions of TMP and TEP were studied by in situ diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) on dry and water-precovered nanoparticles in dark and under simulated solar light irradiation. Two-dimensional correlation analysis of infrared spectra was used to identify surface products as a function of reaction time. The optical properties of the hematite and goethite nanoparticles were investigated with optical spectrophotometry. The optical band gap was determined by analysis of the Tauc relationship around the band gap energy, E-g, yielding band gap energies of 2.14 and 2.28 eV for hematite and goethite nanoparticles, respectively. It is found that both TMP and TEP are readily photodegraded upon solar light irradiation (employing AM1.5 filters with 1735 W m(-2)), yielding surface orthophosphate as the final product. The first step in the dissociation of TMP and TEP is displacement of the methoxy and ethoxy groups, respectively, yielding adsorbed dimethyl phosphate (DMP) and methoxy, and diethyl phosphate (DEP) and ethoxy intermediates. Further photodegradation displaces additional methoxy and ethoxy groups with adsorbed orthophosphate as final reaction product. Methoxy and ethoxy fragments are simultaneously oxidized to carboxylates and carbonates. Photodegradation of TMP and TEP is promoted by OH radicals, which is evidenced by the higher photodegradation rate on water-precovered surfaces. The rate of TMP degradation is higher than that for TEP contrary to what is expected from their corresponding bulk hydrolysis rates, but consistent with their surface reactivity in dark, where TMP is observed to dissociate at room temperature but not TEP (or only very slowly). The photodegradation rate is higher on the goethite nanoparticles than the hematite nanoparticles on both dry and water precovered surfaces. The TMP and TEP photodegradation rate constants are found to be 0.025 (0.058) and 0.008 (0.023) min(-1), respectively, on water-precovered hematite (goethite) nanoparticles.
|
|
| 10. |
|
|
| 11. |
- Wu, Pei-Hsuan, et al.
(författare)
-
Growth and Functionalization of Particle-Based Mesoporous Silica Films and Their Usage in Catalysis
- 2019
-
Ingår i: Nanomaterials. - : MDPI. - 2079-4991. ; 9:4
-
Tidskriftsartikel (refereegranskat)abstract
- We report the formation of mesoporous films consisting of SBA-15 particles grown directly onto substrates and their usage as catalysts in esterification of acetic acid and ethanol. The film thickness was altered between 80 nm and 750 nm by adding NH4F to the synthesis solution. The salt also affects the formation rate of the particles, and substrates must be added during the formation of the siliceous network in the solution. Various substrate functionalizations were tested and hydrophobic substrates are required for a successful film growth. We show that large surfaces (amp;gt; 75 cm(2)), as well as 3D substrates, can be homogenously coated. Further, the films were functionalized, either with acetic acid through co-condensation, or by coating the films with a thin carbon layer through exposure to furfuryl alcohol fumes followed by carbonization and sulfonation with H2SO4. The carbon-coated film was shown to be an efficient catalyst in the esterification reaction with acetic acid and ethanol. Due to the short, accessible mesopores, chemical variability, and possibility to homogenously cover large, rough surfaces. the films have a large potential for usage in various applications such as catalysis, sensing, and drug delivery.
|
|
| 12. |
|
|
