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.
Catalysts2013, 3(4), 978-997; doi:10.3390/catal3040978 - published online 13 December 2013 Show/Hide Abstract
Abstract: In this work, the results of gas phase cyclohexane photocatalytic oxidative dehydrogenation on MoOx/SO4/TiO2 catalysts with DRIFTS analysis are presented. Analysis of products in the gas-phase discharge of a fixed bed photoreactor was coupled with in situ monitoring of the photocatalyst surface during irradiation with an IR probe. An interaction between cyclohexane and surface sulfates was found by DRIFTS analysis in the absence of UV irradiation, showing evidence of the formation of an organo-sulfur compound. In particular, in the absence of irradiation, sulfate species initiate a redox reaction through hydrogen abstraction of cyclohexane and formation of sulfate (IV) species. In previous studies, it was concluded that reduction of the sulfate (IV) species via hydrogen abstraction during UV irradiation may produce gas phase SO2 and thereby loss of surface sulfur species. Gas phase analysis showed that the presence of MoOx species, at same sulfate loading, changes the selectivity of the photoreaction, promoting the formation of benzene. The amount of surface sulfate influenced benzene yield, which decreases when the sulfate coverage is lower. During irradiation, a strong deactivation was observed due to the poisoning of the surface by carbon deposits strongly adsorbed on catalyst surface.
Catalysts2013, 3(4), 966-977; doi:10.3390/catal3040966 - published online 12 December 2013 Show/Hide Abstract
Abstract: X6Al2HT500 hydrotalcites, where X represents Mg, Fe, Cu or Zn were synthetized and investigated before and after gold deposition for toluene and CO total oxidation reactions. The samples have been characterized by specific areas, XRD measurements and Temperature Programmed Reduction. Concerning the toluene total oxidation, the best activity was obtained with Au/Cu6Al2HT500 catalyst with T50 at 260 °C. However, catalytic behavior of Au/X6Al2HT500 sample in both reactions depends mainly on the nature of the support.
Catalysts2013, 3(4), 954-965; doi:10.3390/catal3040954 - published online 3 December 2013 Show/Hide Abstract
Abstract: A variety of primary alcohols and phenols were reacted with acetic anhydride at room temperature in the presence of sodium bicarbonate to produce corresponding esters in good to excellent yields. The acetylation of 4-nitrobenzyl alcohol was also carried out using other bicarbonates and carbonates. The reaction in the presence of cesium bicarbonate and lithium carbonate gave 4-nitrobenzyl acetate in excellent yield, while in the presence of Na2CO3, K2CO3, Cs2CO3, or KHCO3 the yield was in the range of 80%–95%. Calcium carbonate and cobaltous carbonate did not promote the acetylation of 4-ntirobenzyl alcohol using acetic anhydride. The acetylation of 4-nitrobenzyl alcohol was carried out using ethyl acetate, THF, toluene, diethyl ether, dichloromethane and acetonitrile, and gave good yields ranging from 75%–99%. Toluene was the best solvent for the reaction, while diethyl ether was the poorest.