摘要:

In order that a reaction be thoroughly understood, it is necessary to know the concentrations of the reactants. Obtaining such knowledge is not considered a great hurdle in the investigation of homogeneous reactions. With heterogeneous reactions the question of the concentration of the reactant is not always readily answered and, as will be shown, the problem is particularly acute in heterogeneous catalysis, It is necessary to consider the catalyst itself as a reactant in at least one step of the overall reaction. Considering the catalyst a reactant is not only necessary but also fruitful when it is realized that in many cases the catalyst provides the only path whereby a reaction can occur; in such cases it is not merely a substance which increases the rate of a reaction that would occur anyway.

ISSN:0161-4940    

DOI:10.1080/01614947408071855

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

The relationships between the surface properties of ionic salts, in particular metal sulfates, and their catalytic activities have intrigued us for some time [l]. They offer a useful model for linking homogeneous to heterogeneous catalysis. A metal sulfate, for example NiSO4·7H2O, develops a significant degree of acidity-and hence catalytic activity-only after heating causes deaquation. In 1965, on the basis of the physical and chemical characterization of changes accompanying such a process, the mechanism of surface activation was rationalized in terms of an intermediate, mestastable phase formed during the transition from one crystal modification to another [29]. During this change the nickel system exhibits a maximum acidity at an acid strength corresponding to that of 50% H2SO4about half way between the monohydrate and anhydrous form. These acidic sites, attributed to vacant coordination sites on the above intermmediate crystal lattice, are responsible for the catalytic activity of solid metal sulfates.

ISSN:0161-4940    

DOI:10.1080/01614947408071856

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

The concept of surface acidity was originally introduced with the aim of justifying the presence of some substances formed in catalytic chemical reactions, not as a consequence of suppositions about the nature of surface-active sites of solid catalysts. The formation of such substances in some reactions (e.g., cracking, isomerization, or polymerization) can be better explained by admitting the formation of reaction intermediates having the structure of a carbonium ion, which can be formed by interaction between the reacting substance (hydrocarbon) and an acid center. As an example, in the cracking of alkylaromatics catalyzed by decationated zeolites, the following reaction mechanism is generally accepted:

ISSN:0161-4940    

DOI:10.1080/01614947408071857

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

The variety of supported metal catalysts utilized in the operations of the petroleum and chemical industries emphasizes the importance of metal-catalyzed reactions. As a result, many scientific investigators have attempted to characterize and follow closely the changes in the crystallite size and shape of supported metal particles in commercial and simulated environments. From these efforts a massive production of experimental facts has emerged.

ISSN:0161-4940    

DOI:10.1080/01614947408071858

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

Although the catalytic oxidation of inorganic molecules, as well as the oxidation and oxidative dehydrogenation of hydrocarbons, has been the subject of extensive research, the role of oxygen in surface reactions remains uncertain. Various forms of adsorbed oxygen have been proposed on the basis of kinetic and adsorption data or electrical conductivity measurements; yet, very little direct spectroscopic evidence is available apart from that provided by electron spin resonance (ESR) spectroscopy.

ISSN:0161-4940    

DOI:10.1080/01614947408071859

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

Methanation, the hydrogenation of carbon oxides to methane. has been the subject of a large number of catalytic studies during the past 70 years. In the earliest work. that of Sabatier and Senderens [l]. nickel was found to be a very efficient catalyst. Nickel is still the material of choice in most investigations of methanation, although ruthenium, cobalt, and iron are also active.

ISSN:0161-4940    

DOI:10.1080/01614947408071860

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

Supported metal catalysts find wide industrial application. Of the many reasons for their use, none is more important than the very high degree of dispersion of the metal which can be achieved with comparative ease. Much effort has been devoted in recent years to the physical characterization of such catalysts, but it has recently been recognized that the functions of the metal and of the support cannot be readily separated. It has, of course, long been known that the support plays a vital role in dual ._ function catalysts: the phenomenon of hydrogen spillover is a further symptom of the close interaction between metal and support. This article reviews its detection and utilization.

ISSN:0161-4940    

DOI:10.1080/01614947408071861

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

A large amount of research has recently been devoted to oxidative conversions of hydrocarbons, and many laboratories in various countries are concerned with this problem. This field of catalysis has been extensively studied. The new, particularly spectroscopic, experimental methods provide additional information on the structures of surface compounds formed by interactions of various reactants with the catalyst. The very sensitive chromatographic technique has made possible the detection of multiple oxygen compounds yielded by oxidation of hydrocarbons of various structure so that the possibility of various conversion paths has become evident. Many schemes for the catalytic oxidation of hydrocarbons, particularly of olefins and aromatics, have been proposed. Considerably less extensive was the research on the oxidation of alkanes.

ISSN:0161-4940    

DOI:10.1080/01614947408071862

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

Following the first publication by Calvin in 1938 [1], homogeneous catalytic hydrogenation [2–5] has evolved into one of the most intensively studied branches of catalysis. This development has been supported up until now principally by the possibility this “simple” reaction offered for an understanding of some basic problems of catalysis by transition metals. In fact, homogeneous catalytic hydrogenation by transition metal complexes has possibly become the theoretically and mechanistically best known catalytic reaction of this sort.

ISSN:0161-4940    

DOI:10.1080/01614947408071863

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor

摘要:

Catalyst research for ethylbenzene (EB) dehydrogenation has been interest to many chemical manufacturers because styrene monomer is such a large-volume chemical and a steady growth of styrene markets is predicted. EB is relatively easy to dehydrogenate and the reaction may be effected by a simple thermal gas-phase process as observed by Berthelot in 1869 [l]. However, a much higher selectivity to styrene is obtained by contact catalysts. The historical evolution of EB dehydrogenation processes has been summarized by Kearby [21 and others [3].

ISSN:0161-4940    

DOI:10.1080/01614947408071864

出版商:Taylor & Francis Group    

年代:1974

数据来源: Taylor