Catalysts chromium-vanadium

The data on the rate of reaction of o-, m-, and p-xylene over vanadium oxide catalyst and of m-xylene over mixed vanadium oxide catalysts (chromium-vanadium and antimony-vanadium) were correlated with the reaction scheme below by the following rate expressions, which are based on the Langmuir-Hinshelwood mechanisms where the adsorption of m-xylene is strong. 

Metals in the platinum family are recognized for their ability to promote combustion at lowtemperatures. Other catalysts include various oxides of copper, chromium, vanadium, nickel, and cobalt. These catalysts are subject to poisoning, particularly from halogens, halogen and sulfur compounds, zinc, arsenic, lead, mercury, and particulates. It is therefore important that catalyst surfaces be clean and active to ensure optimum performance. 

When a chromium-vanadium oxide and an antimony-vanadium oxide catalyst were used, the atomic ratio of chromium or antimony to vanadium was unity. 

The relative ratios for the formation of m-tolunitrile from m-xylene, ki/kx was nearly the same for both a vanadium and a chromium-vanadium catalyst, but it was higher for an antimony-vanadium catalyst. The increase of kx/kx, which indicates an increase of the degree of single methyl group adsorption for m-xylene, seems to be ascribable to the strength of adsorption and the surface structure of an antimony-vanadium catalyst. 

The major contaminating metals found on catalytic cracking catalyst are vanadium, nickel, copper, chromium, and iron. Small amounts of these metals are present in the crude petroleum and, except for some of the iron, all are in the form of metal-organic compounds. Some of these compounds are volatile and when the vacuum gas oil feed to the catalytic cracking units is prepared, they appear in the gas oil. A fraction of the iron, and probably chromium, found on the catalyst is the result of erosion and corrosion either in the lines or in the equipment. 

Ziegler-Natta Catalysts (Heterogeneous). These systems consist of a combination of a transition metal compound from groups IV to VIII and an organometallic compound of a group I—III metal.23 The transition metal compound is called the catalyst and the organometallic compound the cocatalyst. Typically the catalyst is a halide or oxyhalide of titanium, chromium, vanadium, zirconium, or molybdenum. The cocatalyst is often an alkyl, aryl, or halide of aluminum, lithium, zinc, tin, cadmium, magnesium, or beryllium.24 One of the most important catalyst systems is the titanium trihalides or tetra-halides combined with a trialkylaluminum compound. 

Transition metals have many uses in our society. Iron is used for steel copper for electrical wiring and water pipes titanium for paint silver for photographic paper manganese, chromium, vanadium, and cobalt as additives to steel platinum for industrial and automotive catalysts and so on. 

We have investigated a series of the dehydrogenating catalysts for this reaction. Our attention was focused on two of them. Further study of 2,3-butanediol dehydrogenation and oxidative dehydrogenation to butadione was performed using zinc-chromium oxide catalysts and vanadium-magnesium oxide catalysts as well. 

The conversion of methane into formaldehyde, ethylene, and higher hydrocarbons by a process of oxidation has been claimed.1 - A mixture ot air and methane is heated in the presence ot a copper gauze catalyst under pressure to give formaldehyde, which by reaction with methane forms ethylene with removal of water in the presence of catalysts of iron, cobalt, nickel, chromium, vanadium, etc., at 500° C.—and under extremely high pressures. 

As in all conversions of this type, which are autocatalytic, the induction period is relatively long. Catalysts are used to shorten it. These catalysts are soluble salts of cobalt, chromium, vanadium or manganese, usually acetates. The oxidation rate rises with the number of carbon atoms in the hydrocarbon and with the extent to which the chain is linear. Thus, if it is l for ethane, it is as high as 100 for propane, 500 for n-butane and 1000 for n-pentane. 

In certain commercial catalysts, nickel sulfide is used in admixture with sulfides of chromium, vanadium, molybdenum, or tungsten. There is no information available on these mixed sulfide catalysts. It can be conjectured that the nickel sulfide reacts with the other sulfides to form thio salts such as NiCr2S , NiMoSs, etc., and that either these thio salts act as stabilizing supports for Ni3S2 catalyst, or are catalysts themselves. 

Karamullaoglu G, Dogu T (2007) Oxidative dehydrogenation of ethane over chromium — vanadium mixed oxide and chromium oxide catalysts. Ind Eng Chem Res 46 7079-7086... 

KaramuUaoglu, G., Onen, S., and Dogu, T. Oxidative dehydrogenation of ethane and isohutane with chromium-vanadium-niohium mixed oxide catalysts. Ghent. Eng. Process. 2002, 41, 331. 

Catalysts used in the polymerization process. For example, commercial isotactic polypropylene is polymerized from a hetereogenous organo-aluminium-titanium complex (Ziegler-Natta process) [110,1260], or less frequently from metallic oxides of chromium, vanadium or molybdenum bonded to an inert support (e.g. the Philips process) [447]. Transition metal ion contents vary in different commercial samples (Table 2.4). 

From about 1950, Shell 205 and similar catalysts based on alkalized iron and chromium oxides were used exclusively for styrene productioa As plant capacities were rapidly expanded, efforts were increased to improve the performance of the catalyst. Higher potash levels were introduced and cement binders were used to increase strength and selectivity. Ethylbenzene conversion, which was still about 30-50% in the 1950 s, was increased to at least 60% by 1960. Better plant designs were developed and reactors with up to three beds were introduced. One of the first higher selectivity catalysts included vanadium pentoxide with the conventional chromium oxide and potash. Improvements often led to different catalysts being used in a single reactor to optimize operation. 

Like all components, the electrode structure has evolved over time, and now a carbon-supported heterogeneous catalyst of platinum or platinum alloys with other metals such as chromium, vanadium, or cobalt is commonly used [40]. Similar to PEFC electrodes, precious metal catalyst loading of around 0.25 on the anode to 0.5 mg/cm are used. Although platinum is the base catalyst material, it is not a major contributor to the cost... 

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