摘要:

Since many free radical intermediates are postulated in catalytic mechanisms [l] and since many of the commercially important catalysts are supported transition metal compounds [2], the method of electron paramagnetic resonance (EPR) should be a useful tool for the study of catalytic processes.

ISSN:0161-4940    

DOI:10.1080/01614947408075368

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

Recent studies from this laboratory [l, 2] on the reaction mechanism of the pentose phosphate pathway in rabbit and rat liver cells have accentuated the role of enzyme-catalyzed exchange reactions as a means by which tracer carbon is relocated in the absence of a net metabolic flux. While this is an intrinsic property of the group transferring enzymes of the pathway and is seen as a deleterious property of14C for the mapping and quantitation of metabolic pathways, it has re-emphasized the possible usefulness of isotope exchange reactions in understanding the mechanism of action of nature's catalyst.

ISSN:0161-4940    

DOI:10.1080/01614947408075369

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

Perhaps the most difficult practical problem in the study of catalysis is presented by the loss of catalyst activity during reaction. This very complicated phenomenon is made even more confusing by the wide variety of deactivation phenomena and the lack of systematization in this field of research. Consequently little fundamental work has been done on systems in which the catalyst is subject to deactivation. This review proposes to focus on one broad type of catalyst deactivation which also happens to be the most common type of deactivation found in practice.

ISSN:0161-4940    

DOI:10.1080/01614947408075370

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

In the last fifteen years, there have been considerable changes in and additions to our understanding of chemisorption. Before this time, surfaces were usually pictured as homogeneous, and it was generally believed that one binding energy characterized adsorption at a particular coverage and that the heat of adsorption varied strongly with coverage. While desorption processes usually were found to obey Arrhenius expressions, pre-exponential factors showed wide and unpredictable variations. Similarly condensation kinetics could only be described in vague terms as occurring through either site occupation or precursor-controlled kinetics, but there was no concensus as to the details of the energy transfer process or the potential surfaces involved.

ISSN:0161-4940    

DOI:10.1080/01614947408075371

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

It is a pleasure to receive the second Paul H. Emmett Award in Fundamental Catalysis and to have the opportunity to present this address. The subject, catalysis by metals, is one in which Professor Emmett himself has contributed extensively. His long-standing interest in the iron catalysts for ammonia synthesis, and also his later interest in metal alloy catalysts, are well known.

ISSN:0161-4940    

DOI:10.1080/01614947408075372

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

It is well known that in the practical employment of catalysts in commercial reactors, physical processes may play an important and even dominant role in the overall conversion scheme. Such physical processes may include mass transfer both within and external to the catalyst particles and the analogous effects of heat transport. In addition, for packed beds, dispersion of mass and heat in both the axial and radial directions may be important. The intra-particle effects arise because of the significant size of the catalyst particles which in turn is dictated by the requirement that the pressure drop within the reactor shall not be excessive. In practice, catalyst pellets up to about 1 cm in diameter are often employed.

ISSN:0161-4940    

DOI:10.1080/01614947408075373

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

Supported metal catalysts are widely used because it is possible to prepare them in a highly dispersed form, consisting of very small microcrystals, which provide a maximum available surface area for the catalytic reaction [1]. Superficially, one might expect that the effectiveness of the material as a catalyst would be simply proportional to the surface area. In this case the specific catalytic activity would be independent of the size of the microcrystals. Size-independent specific activity is observed in a number of reactions, such as hydrogenation of benzene on alumina-supported platinum [2]. For other reactions, the specific catalytic activity is dependent on the size of the mircrocrystals. It is possible that the surface of a very small microcrystal is either more or less active than that of a larger crystal. Figure 1 shows the specific activity of the catalyst for deuteration of benzene and for hydrogen exchange with benzene on nickel catalysts [3]. Note that the smaller microcrystals are more active than the larger crystals for the hydrogenation reaction, but the smaller microcrystals are less effective for the exchange reaction. Such observations can be discussed in terms of the number and nature of the surface sites on a microcrystal [3—5].

ISSN:0161-4940    

DOI:10.1080/01614947408075374

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

It is generally accepted nowadays that catalysis occurring at the surface of a metal compound, such as an oxide or a sulfide, can be described in terms of the properties of the. metal ions, surrounded by ligands, on the surface of the catalyst. It is one of the attractions and also the challenge of catalytic research to find what structure on the surface causes the metal ion to be active. With the commonly used heterogeneous catalysts, the metal ion is found on the surface in conditions which vary in valency as well as in ligand surroundings. It is therefore difficult to determine what configuration is actually responsible for the catalytic activity.

ISSN:0161-4940    

DOI:10.1080/01614947408075375

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

Most heterogeneous catalysts are either supported on some kind of porous material or the catalyst itself is porous. To satisfy practical constraints such as pressure drop, handling, and separation from products, these catalysts are generally pelletized. Very often the overall chemical reaction rates within these catalyst pellets are determined by a complicated interaction of internal and external transport effects with the intrinsic kinetic rate at the active surface.

ISSN:0161-4940    

DOI:10.1080/01614947408075376

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

For some time it has been recognized, at least implicitly, that catalysis and catalytic reaction engineering, both a mixture of art and science, enjoy a common synergistic basis, within which both the science and applied sciences (engineering) owe a debt to each other. While one might argue with respect to the relative merits of the contributions from one side of the issue or the other, we suggest that a respect for both aspects of this complex subject- the fundamentals (science) and their application (engineering), can only yield benefit to all concerned-the catalytic scientist and the catalytic reaction engineer.

ISSN:0161-4940    

DOI:10.1080/01614947408075367

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor