Catalysts2014, 4(2), 89-115; doi:10.3390/catal4020089 - published online 15 April 2014 Show/Hide Abstract
Abstract: Benzyl alcohol oxidation was carried out in toluene as solvent, in the presence of the potentially inhibiting oxidation products benzaldehyde and benzoic acid. Benzoic acid, or a product of benzoic acid, is identified to be the inhibiting species. The presence of a basic potassium salt (K2CO3 or KF) suppresses this inhibition, but promotes the formation of benzyl benzoate from the alcohol and aldehyde. When a small amount of water is added together with the potassium salt, an even greater beneficial effect is observed, due to a synergistic effect with the base. A kinetic model, based on the three main reactions and four major reaction components, is presented to describe the concentration-time profiles and inhibition. The inhibition, as well as the effect of the base, was captured in the kinetic model, by combining strong benzoic acid adsorption and competitive adsorption with benzyl alcohol. The effect of the potassium salt is accounted for in terms of neutralization of benzoic acid.
Catalysts2014, 4(2), 77-88; doi:10.3390/catal4020077 - published online 31 March 2014 Show/Hide Abstract
Abstract: In this study, we presented the synthesis of LaNi0.3Co0.7O3−δ (LNCO) and SrCo0.8Fe0.2O3−δ (SFCO) perovskites and their catalytic reactivity under CO gas flow. The synthesis method is based on the complexation method combining ethylenediaminetetraacetic acid (EDTA)-citrate. The as-prepared materials were characterized using X-ray diffraction/Rietveld refinement and electron microscopy. The diffractograms and Rietveld refinement showed that the EDTA-citrate method allows us to obtain monophasic powders with submicronic size. The structural analyses revealed different morphologies linked to the crystallinity of LNCO and SFCO, and to the mean crystallite size. The catalytic performances of LNCO and SFCO were studied in situ by Fourier Transform InfraRed spectrometer as a function of time and temperature. The catalytic process gave rise to total oxidation with carbon dioxide and water production. LNCO and SFCO exhibit the same profile for catalytic activity with a conversion rate of twice as high for LNCO. Below 150 °C, the kinetic conversion is slow, but beyond this temperature they reach rapidly the complete transformation at 250 °C and 275 °C for LNCO and SFCO, respectively.
Catalysts2014, 4(1), 49-76; doi:10.3390/catal4010049 - published online 11 March 2014 Show/Hide Abstract
Abstract: This focused review article underscores how metal reduction promoters can impact deactivation phenomena associated with cobalt Fischer-Tropsch synthesis catalysts. Promoters can exacerbate sintering if the additional cobalt metal clusters, formed as a result of the promoting effect, are in close proximity at the nanoscale to other cobalt particles on the surface. Recent efforts have shown that when promoters are used to facilitate the reduction of small crystallites with the aim of increasing surface Co0 site densities (e.g., in research catalysts), ultra-small crystallites (e.g., <2–4.4 nm) formed are more susceptible to oxidation at high conversion relative to larger ones. The choice of promoter is important, as certain metals (e.g., Au) that promote cobalt oxide reduction can separate from cobalt during oxidation-reduction (regeneration) cycles. Finally, some elements have been identified to promote reduction but either poison the surface of Co0 (e.g., Cu), or produce excessive light gas selectivity (e.g., Cu and Pd, or Au at high loading). Computational studies indicate that certain promoters may inhibit polymeric C formation by hindering C-C coupling.
Catalysts2014, 4(1), 38-48; doi:10.3390/catal4010038 - published online 5 March 2014 Show/Hide Abstract
Abstract: Gold nanoparticles have been proven to act as efficient catalysts for chemical reactions, such as oxidation and hydrogen production. In this review we focus on a different aspect of the catalysis of gold nanoparticles; single-walled carbon nanotube (SWCNT) synthesis. This is not a traditional meaning of catalytic reaction, but SWCNTs cannot be synthesized without nanoparticles. Previously, gold was considered as unsuitable metal species as the catalyst of SWCNT synthesis. However, gold nanoparticles with diameters smaller than 5 nm were found to effectively produce SWCNTs. We discuss the catalysis of gold and related metals for SWCNT synthesis in comparison with conventional catalysts, such as iron, cobalt, and nickel.
Catalysts2014, 4(1), 1-35; doi:10.3390/catal4010001 - published online 6 January 2014 Show/Hide Abstract
Abstract: The application of enzymes such as laccase and xylanase for the preparation of cellulose from lignocellulosic material is an option for those industries seeking to reduce the use of chlorine-containing bleach agents, thus minimizing the environmental impact of their processes. Mixed hydrolytic and oxidative enzyme systems have been well described in the context of biopulping, and thus provide good precedent regarding effectiveness, despite the susceptibility of xylanase to inactivation by laccase-generated oxidants. This paper examines the progress towards development of sequential and simultaneous mixed enzyme systems to accomplish delignification.