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Sökning: hsv:(NATURVETENSKAP) hsv:(Kemi) hsv:(Fysikalisk kemi) > Högskolan i Borås

  • Resultat 1-10 av 18
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1.
  • Mohsenzadeh, Abas, et al. (författare)
  • The Effect of Carbon Monoxide Co-Adsorption on Ni-Catalysed Water Dissociation
  • 2013
  • Ingår i: International Journal of Molecular Sciences. - : M D P I AG. - 1661-6596 .- 1422-0067. ; 14:12, s. 23301-23314
  • Tidskriftsartikel (refereegranskat)abstract
    • The effect of carbon monoxide (CO) co-adsorption on the dissociation of water on the Ni(111) surface has been studied using density functional theory. The structures of the adsorbed water molecule and of the transition state are changed by the presence of the CO molecule. The water O–H bond that is closest to the CO is lengthened compared to the structure in the absence of the CO, and the breaking O–H bond in the transition state structure has a larger imaginary frequency in the presence of CO. In addition, the distances between the Ni surface and H2O reactant and OH and H products decrease in the presence of the CO. The changes in structures and vibrational frequencies lead to a reaction energy that is 0.17 eV less exothermic in the presence of the CO, and an activation barrier that is 0.12 eV larger in the presence of the CO. At 463 K the water dissociation rate constant is an order of magnitude smaller in the presence of the CO. This reveals that far fewer water molecules will dissociate in the presence of CO under reaction conditions that are typical for the water-gas-shift reaction.
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2.
  • Tian, Bo-Xue, et al. (författare)
  • Catalytic Mechanism of Porphobilinogen Synthase : The Chemical Step Revisited by QM/MM Calculations
  • 2012
  • Ingår i: Journal of Physical Chemistry B. - : American Chemical Society. - 1520-6106 .- 1520-5207. ; 116:40, s. 12105-12112
  • Tidskriftsartikel (refereegranskat)abstract
    • Porphobilinogen synthase (PBGS) catalyzes the asymmetric condensation and cyclization of two 5-aminolevulinic acid (5-ALA) substrate molecules to give porphobilinogen (PBG). The chemical step of PBGS is herein revisited using QM/MM (ONIOM) calculations. Two different protonation states and several different mechanisms are considered. Previous mechanisms based on DFT-only calculations are shown unlikely to occur. According to these new calculations, the deprotonation step rather than ring closure is rate-limiting. Both the C–C bond formation first mechanism and the C–N bond formation first mechanism are possible, depending on how the A-site ALA binds to the enzyme. We furthermore propose that future work should focus on the substrate binding step rather than the enzymatic mechanism.
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4.
  • Mohsenzadeh, Abas, et al. (författare)
  • Hydrocarbon combustion and synthesis on Ni(111), Ni(110) and Ni(100) surfaces : A comparative density functional theory study
  • 2014
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • Combustion and synthesis of hydrocarbons may occur directly (CH → C + H and CO → C + O) via a formyl intermediate (CH + O → CHO followed by CHO → CO + H and CO + H → CHO followed by CHO → CH + O) . The activation and reaction energies of these reactions on the Ni(111), Ni(110) and Ni(100) surfaces were investigated using density functional theory (DFT). Calculations show that the barriers are sensitive to the surface structure. The barrier for CH dissociation (catalytic hydrocarbon combustion) is lower than that of for its oxidation reaction (CH + O → CHO) on the Ni(110) and Ni(100) surfaces. In contrast, the barrier for oxidation is lower than that for dissociation on the Ni(111) surface. This means CH will preferably dissociate on the Ni(110) and Ni(100) surfaces, but not on the Ni(111) surface. The barrier for dissociation increases in the order Ni(110) < Ni(100) < Ni(111). The barrier of CHO dissociation to CO and H is almost the same on the Ni(111) and Ni(110) surfaces and it is lower compared to the Ni(100) surface. The energy barrier for carbon monoxide dissociation (catalytic hydrocarbon synthesis) is higher than that of for its hydrogenation reaction on all three surfaces. This means that the hydrogenation to CHO favored over the nickel surfaces studied here. The barrier for both reactions increases in the order Ni(110) < Ni(100) < Ni(111). Formyl dissociation to CH + O barrier is the lowest on the Ni(110) surface and follows the order Ni(100) > Ni(111) > Ni(110). Our DFT results show that the Ni(110) surface has a larger catalytic activity compared to the other surfaces, and that Ni is a better catalyst for hydrocarbon combustion than synthesis.
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5.
  • Mohsenzadeh, Abas, et al. (författare)
  • Oxidation and dissociation of formyl on Ni(111), Ni(110) and Ni(100) surfaces : A comparative density functional theory study
  • 2014
  • Konferensbidrag (refereegranskat)abstract
    • Formyl (CHO) is an important adsorbate and a key intermediate in industrial processes such as water gas shift (WGS), Fischer Tropsch synthesis (FTS) and catalytic hydrocarbon combustion reactions. Density functional theory (DFT) with the PBE functional was used to calculate the adsorption, reaction and activation energies of formyl oxidation and dissociation on Ni(111), Ni(110) and Ni(100) surfaces. The results show that these energies are sensitive to the surface structure. The dissociation barrier for CHO → CH + O (FTS process) is higher than that for CHO → CO + H (catalytic combustion) on all three surfaces. This means that the dissociation to CO and H is kinetically favored. The dissociation reaction rate decreases in the order Ni(110) > Ni(111) > Ni(100) for both dissociation reactions. The formation of formate (CHO + O → HCOO), which is included in one of the pathways for the WGS reaction, has lowest activation energy on the Ni(111) surface, and the energy increases in the order Ni(111) < Ni(110) < Ni(100). However, the reaction rate at 463 K, which is a typical temperature for industrial processes that involve these reactions, is at least five orders of magnitude higher for the CHO → CO + H reaction than for the other two reactions, irrespective of the crystallographic structure of the Ni surface. This means that Ni surfaces studied here are better catalysts for this reaction. The results also show that the WGS reaction on a Ni catalyst does not primarily occur via the formate pathway.
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6.
  • Biswas, Tuser, 1988-, et al. (författare)
  • Effective Pretreatment Routes of Polyethylene Terephthalate Fabric for Digital Inkjet Printing of Enzyme
  • 2021
  • Ingår i: Materials Science & Engineering. - : Wiley. - 0921-5107 .- 1873-4944.
  • Tidskriftsartikel (refereegranskat)abstract
    • Enzymes immobilized on synthetic polyethylene terephthalate (PET) textile surface by resource‐efficient inkjet printing technology can promote developments for various novel applications. Synthetic fabrics often require adequate pretreatments to facilitate such printing process. This work discusses PET–woven fabric pretreatment routes to improve wettability by alkaline, enzymatic, and plasma processes for effective printing of lysozyme using an industrial piezoelectric printhead. Results indicate that all pretreated samples contain a similar amount of enzymes upon printing. Plasma treated fabrics show relatively more hydrophilic surface characteristics, better protein binding stability, and lower retained activity. Alkali and cutinase‐treated samples possess relatively higher activity due to the greater amount of enzyme desorption to substrate solution. Depending on respective enzyme‐binding stability, a combination of a well-pretreated surface and inkjet as preferential placement technology, the approach of this study can be used as a facile enzyme immobilization method for suitable applications, for example, controlled‐release and bio‐sensing.
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7.
  • Biswas, Tuser, 1988-, et al. (författare)
  • Sequential Inkjet Printing of Lysozyme and Tyrosinase on Polyamide Fabric: Sustainable Enzyme Binding on Textile Surface
  • 2022
  • Ingår i: Advanced Materials Interfaces. - : John Wiley & Sons. - 2196-7350. ; 9:22
  • Tidskriftsartikel (refereegranskat)abstract
    • An ink containing tyrosinase catalyzes the tyrosine residues on lysozyme protein to bind it on a plasma-treated polyamide-6,6 (PA) fabric. Inkjet printing enables controlled and sequential deposition of two enzymes on PA which is necessary for proper binding. The effect of different printing sequences on crosslinking stability and enzymatic activity is presented. The lysozyme bound on the fabric shows satisfactory antimicrobial activity. The printed fabric retains about 68% of the ink activity when tyrosinase is printed before lysozyme. Further, this fabric retains about 24% of the initial activity up to four reuses. The fabric shows acceptable inhibition of bacterial growth and retains almost half of its initial activity when cold stored for a month. This work shows the potential of protein binding on textile surface using various means of sustainable technologies, namely enzyme, inkjet, and plasma. 
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8.
  • Börjesson, Anders, et al. (författare)
  • Modelling of Ostwald ripening of metal clusters attached to carbon nanotubes
  • 2011
  • Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society. - 1932-7447 .- 1932-7455. ; 115:50, s. 24454-24462
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a model of Ostwald ripening of nanosized clusters and apply it to study the time evolution of metal particles attached to carbon nanotubes. The Ostwald ripening of metal clusters attached to carbon nanotubes differs from that of free metal clusters. While free clusters experience a rapid broadening in the size dispersion, this may be delayed by the nanotubes, which may therefore limit the ripening. The diameter and chirality of the carbon nanotubes were also seen to affect the Ostwald ripening of the catalyst particles. For a collection of carbon nanotubes that contains different diameters and chiralities, the clusters attached to carbon nanotubes with large diameters and strong carbon–metal adhesion are the most likely to survive the Ostwald ripening.
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  • Resultat 1-10 av 18

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