Showing papers in "Catalysis Reviews-science and Engineering in 2005"
TL;DR: In this paper, a review of the synthesis of mixed oxides by various conventional and non-conventional methods and their characterization by several techniques, as reported in the literature, are assessed.
Abstract: This is the first review of titanium dioxide‐zirconium dioxide (TiO2‐ZrO2) mixed oxides, which are frequently employed as catalysts and catalyst supports. In this review many details pertaining to the synthesis of these mixed oxides by various conventional and nonconventional methods and their characterization by several techniques, as reported in the literature, are assessed. These mixed oxides have been synthesized by different preparative analogies and were extensively characterized by employing various spectroscopic and nonspectroscopic techniques. The TiO2‐ZrO2 mixed oxides are also extensively used as supports with metals, nonmetals, and metal oxides for various catalytic applications. These supported catalysts have also been thoroughly investigated by different techniques. The influence of TiO2‐ZrO2 on the dispersion and surface structure of the supported active components as examined by various techniques in the literature has been contemplated. A variety of reactions catalyzed by TiO2‐ZrO2 and su...
280 citations
TL;DR: In this article, it was shown that at least four different catalytic sites are required to interpret experimental observations in contrast with a dual site site concept, which only considered two sites.
Abstract: A high level of hydrodenitrogenation (HDN) is required to achieve a desirable conversion of other hydroprocessing reactions. This results from a strong adsorption of nitrogen‐containing compounds on catalytic sites that slows down the hydrogen activation process and hinders the adsorption of other reactants. Studies on model compounds and real feeds indicate that less than 50 ppm of nitrogen in the feed can poison catalytic sites. Kinetic studies determined adsorption constants of various nitrogen‐containing compounds and concluded that at least four different catalytic sites are required to interpret experimental observations in contrast with a dual site site≅concept, which only considered two sites. The advancements in experimental techniques allowed identification of products formed during very early stages of hydrodenitrogenation. These results confirmed that the removal of the amino group from saturated amines, as the last step in hydrodenitrogenation, is governed by the type of carbon to which the a...
233 citations
TL;DR: Asymmetric heterogeneous catalysis is a vivid branch of catalysis, remaining, however, largely a domain of organic chemists as mentioned in this paper The view towards asymmetric heterogenous catalysis adopted in this review is mainly from catalytic science and engineering Not only reaction mechanisms, but also catalytic properties, kinetic regularities, as well as chemical engineering aspects, are covered with the main focus on recent developments
Abstract: Asymmetric heterogeneous catalysis is a vivid branch of catalysis, remaining, however, largely a domain of organic chemists The view towards asymmetric heterogeneous catalysis adopted in this review is mainly from catalytic science and engineering Not only reaction mechanisms, but also catalytic properties, kinetic regularities, as well as chemical engineering aspects, are covered with the main focus on recent developments
223 citations
TL;DR: In this article, a review of the important industrial reaction of formaldehyde manufacture by methanol oxidation over iron molybdate catalysts is presented, where detailed reference is made to the used catalyst, preparation techniques (coprecipitation, sol-gel like, mechanical mixing, etc.) including unsupported and supported catalysts, promoters and characterization methods.
Abstract: This review deals with the important industrial reaction of formaldehyde manufacture by methanol oxidation over iron molybdate catalysts. Detailed reference is made to the used catalyst, preparation techniques (coprecipitation, sol‐gel like, mechanical mixing, etc.) including unsupported and supported catalysts, promoters and characterization methods. The controversial active phase assignment (stoichiometric versus Mo rich iron molybdate) is discussed. The proposed reaction mechanisms and kinetic laws for the main and side reactions are examined. The catalyst deactivation processes are reviewed and the role of Mo excess on these processes is underlined. Finally conclusions and perspectives are presented.
214 citations
TL;DR: In this paper, a comprehensive overview of the state-of-the-art on reforming technology applicable to the development of small scale reformers is presented, including the current production status, the future needs and the advantages of decentralized hydrogen production vs its centralized generation in large capacity plants.
Abstract: Hydrogen production has been a matter of great importance in the last decades, but a renewed interest in its production processes has emerged recently driven by the spectacular advances in fuel cell technology. This review provides a comprehensive overview of the state‐of‐the‐art on reforming technology applicable to the development of small scale reformers. It considers some general aspects on hydrogen production technologies including the current production status, the future needs, and the advantages of decentralized hydrogen production vs its centralized generation in large capacity plants. Conventional and novel technologies are presented together with the new trends in research and development activities.
155 citations
TL;DR: In this article, the rate coefficients of these steps are modeled based upon transition state theory and statistical thermodynamics, and the single event concept explicits the effect of structure on the entropy contribution to the rate coefficient of the transformation.
Abstract: Kinetic models for complex processes may contain an excessive number of rate parameters. Rather than simplifying the reaction scheme the approach illustrated here develops it in terms of the elementary steps of cation chemistry, using a computer algorithm. The resulting scheme, although gigantic, thus consists of a limited number of types of steps, generally involving series of homologous species. The rate coefficients of these steps are modeled based upon transition state theory and statistical thermodynamics. The single event concept explicits the effect of structure on the entropy contribution to the rate coefficient of the transformation, while the enthalpy effect is calculated using the Evans‐Polanyi relation. Together with thermodynamic constraints this approach drastically reduces the number of independent parameters to be determined from the experimental data. The approach is applied to the methanol‐to‐olefins process on ZSM5 and to a process with complex feedstock like the catalytic cracking of v...
126 citations
TL;DR: The potentialities of mesoporous materials both as catalysts and catalytic supports in reactions like alkylation, hydrogenation, and oxidation of various substrates are reviewed in this article.
Abstract: The potentialities of mesoporous materials both as catalysts and catalytic supports in reactions like alkylation, hydrogenation, and oxidation of various substrates are reviewed. Much of our current research effort is devoted to exploring the mechanistic aspects of the reactions, the role of the catalyst structure, and to characterizing the active sites.
64 citations