Showing papers in "Catalysis Reviews-science and Engineering in 1996"

Catalytic Properties of Ceria and CeO2-Containing Materials

Abstract: Over the past several years, cerium oxide and CeO2-containing materials have come under intense scrutiny as catalysts and as structural and electronic promoters of heterogeneous catalytic reactions. Recent developments regarding the characterization of ceria and CeO2-containing catalysts are critically reviewed with a special focus towards catalyst interaction with small molecules such as hydrogen, carbon monoxide, oxygen, and nitric oxide. Relevant catalytic and technological applications such as the use of ceria in automotive exhaust emission control and in the formulation of SO x reduction catalysts is described. A survey of the use of CeO2-containing materials as oxidation and reduction catalysts is also presented.

Sulfated Zirconia-Based Strong Solid-Acid Catalysts: Recent Progress

Abstract: This review article deals with recent progress in the preparation of sulfated zirconia (SZ)-bassed, strong solid-acid catalysts, the characterization of their physicochemical properties and the evaluation of their catalytic performance in various promising applications. Strong emphasis was put on discussion of controversial issues such as the strength of acid sites, the nature of active sites, the reaction mechanism, and the role and state of supported platinum. An important part of this work was devoted to recent catalytic applications.

Basic zeolites : Characterization and uses in adsorption and catalysis

Abstract: The presence of basic centers in some oxides has been recognized for a long time as being important in catalysis [1-4]. Usually both basic and acid sites exist simultaneously. The two centers may work independently or in a concerted way. For instance, in alcohol transformation, dehydration is favored on acidic sites and dehydrogenation on basic centers [3,5]. A large variety of materials are cited as having basic character. They include single-metal oxides (MgO, CaO, ZnO), supported alkali metals (Na/MgO, K/K2CO3), mixed-metal oxides (MgO-A12O3, ZnO-SiO2, MgO-TiO2), zeolites (X and Y saturated with alkaline cations of low electronegativity), hydrotalcite-type anionic clays, asbestoslike materials, carbon-supported basic catalysts, and basic organic resins. ∗ Present address: 16 rue Francois Gillet, 69003 Lyon, France.

Key Aspects of Catalyst Design for the Selective Oxidation of Paraffins

Abstract: This review examines some aspects in the development of heterogenous catalysts for the oxyfunctionalization of light paraffins. Particular attention is devoted to the raction of paraffin oxydehydrogenation to olefins and of n-butane oxidation to maleic anhydride. Most catalyst compositions are based on vanadium oxide as the main component, and the peculiar properties of this element with respect to the catalytic performance are discussed. These properties are also examined in ligh of the stability of the product of partial oxidation towards consecutive unselective oxidation reactions, and with respect to the mechanism of paraffin activation.

Reverse-Flow Operation in Fixed Bed Catalytic Reactors

Abstract: Introduction Transition from the usual steady-state mode of continuous processes toward forced unsteady-state conditions (FUSC) has been discussed in chemical engineering literature since the beginning of the 1960s [1-12]. FUSC can be created by periodic variations of temperature, composition, or other parameters to the inlet of a chemical unit.

A review of deep hydrodesulfurization catalysis

Abstract: Introduction The increasing importance of hydrodesulfurization (HDS) in petroleum processing in order to produce clean-burning fuels has led to a surge of research on the chemistry and engineering of HDS. Most of the earlier works are focused on catalyst characterization by physical methods; on low-pressure reaction studies of compounds like thiophene having relatively high reactivities; on process development; or on CoMo, NiMo, or NiW catalysts supported on alumina, often doped by fluorine or phosphorus. Almost all the reviews have concentrated on alumina-supported CoMo, NiMo, and NiW sulfide catalysts for hydrotreating. Even reviews that are not limited to the above catalytic systems essentially deal with studies of simple compounds like thiophene.

Hydrogen Transfer, Coke Formation, and Catalyst Decay and Their Role in the Chain Mechanism of Catalytic Cracking

Abstract: Introduction Understanding of the process of hydrogen redistribution in catalytic cracking has long been recognized as essential to understanding of the coking processes responsible for catalyst decay. Hydrogen redistribution is also thought to be behind the puzzling excess of paraffins over olefins that has been noted by several authors [1-3], and to hold the key to determining the selectivity of cracking reactions. If the transfer of hydrogen during catalytic cracking can be understood and quantified, much of the detail of the overall process should become clear.

Remote control of catalytic sites by spillover species: A chemical reaction engineering approach

Abstract: Introduction Evidence has accumulated in the last 20 years that spillover processes play a crucial role in many catalytic phenomena. Four symposia have highlighted the advances of knowledge in this area, and the progressive recognition that the phenomena have extremely important consequences (Delmon et al., 1973; Inui et al., 1993; Pajonk et al., 1983; Steinberg, 1989). In spite of this, very few kinetic models incorporating spillover have been presented. Little attention, if any, is given to these phenomena in the design of processes or in the definition of operating conditions. ∗Review based on a lecture presented at the 13th Colloquim on Chemical Reaction Engineering (13 CCRE), held in Windsor Castle, U.K., and jointly organized by the Working Parties “Chemical Reaction Engineering” and “Chemical Engineering in the Applications of Catalysis” of the European Federation of Chemical Engineering.

Low-temperature coupling of methane

Abstract: Introduction Methane is the main component of natural gas and its utilization amounts to ca. 1.7 × 109 tons of oil equivalent per year [1]. Since the present reserve of methane is located in remote places, its transportation is a major problem. Methane coupling to form C2+ hydrocarbons is, therefore, of a primary importance because before transportation methane should be converted into hydrocarbons with higher boiling points, such as ethane, propane, etc. The catalytic conversion of methane can be carried out in several ways which have excellently been reviewed in Refs. 1 and 2. Basically, three routes exist: (i) the indirect route in which methane is first converted into syngas in presence of water (steam reforming), CO2 (carbon dioxide reforming), or oxygen (partial oxidation) and the resultant syngas can be utilized in the traditional way; (ii) direct coupling in the presence of oxygen (oxidative coupling of methane, OCM) or hydrogen (two-step polymerization); and (iii) direct conversion in the presenc...

Measurement of the Effective Diffusivity in Porous Media by the Diffusion Cell Method

Abstract: Introduction There has been a vast amount of investigation in the field of experimental and theoretical treatments of the effective diffusivity in porous media for more than half of a century [1-4]. The effective diffusivity is required for several reasons [5]; for example, during catalyst formulation, active species can be laid down precisely or with specified concentration profiles on a porous matrix or support. In experimental work on heterogeneous reactions an effective diffusivity is needed to obtain the value of the Thiele modulus and hence to determine the intrinsic reaction kinetics. In reactor design the diffusivity is needed to evaluate the Thiele modulus, which can then be an aid in predicting reaction rates for heterogeneous systems. In addition, a simple and quick testing method could be used as a screening or quality control procedure during catalyst manufacture. ∗ On leave from the Department of Chemical Engineering, Kyungnam University, Masan 631-701, Korea.

Catalytic Dimerization of Alkyl Acrylates

Abstract: The review deals with the chemistry of dimerization of acrylic esters in the presence of various catalysts. The article covers literature from 1963 through early 1995. The dimerization reactions are divided into three categories depending on the type of catalyst used, namely, phosphine-catalyzed, metal-catalyzed, and miscellaneous catalysts. Phosphine catalyzed dimerization leads to branched or head—tail dimers. Metal catalyzed dimerization deals with the reactions that take place in the coordination sphere of the transition metals (Ni, Pd, Ru, and Rh) complexes and are aimed at linear or tail—tail dimers. The tail—tail dimers, dialkyl hexenedioates, have a commercial potential as precursors of adipic acid, which is a raw material in the manufacture of nylon-6,6. Various strategies involved in designing the transition metal catalysts for tail—tail dimerization are highlighted. A miscellaneous catalyst section deals with systems that are not covered under the above two categories. It describes cat...