Oxide-based catalysts alumina

The same authors (77) also investigated the Michael addition of nitromethane to a,/l-unsaturated carbonyl compounds such as methyl crotonate, 3-buten-2-one, 2-cyclohexen-l-one, and crotonaldehyde in the presence of various solid base catalysts (alumina-supported potassium fluoride and hydroxide, alkaline earth metal oxides, and lanthanum oxide). The reactions were carried out at 273 or 323 K the results show that SrO, BaO, and La203 exhibited practically no activity for any Michael additions, whereas MgO and CaO exhibited no activity for the reaction of methyl crotonate and 3-buten-2-one, but low activities for 2-cyclohexen-l-one and crotonaldehyde. The most active catalysts were KF/alumina and KOH/alumina for all of the Michael additions tested. 

The sulfur oxidation is carried out at pressure higher than 8 atm and below 180 °C, with a proprietary supported-Mo oxide-based catalyst, for example, an alpha alumina-supported MgMo04 catalyst, operating at 110 °C and 17 atm [59c]. All the products produced by oxidation side reactions and by hydroperoxide reduction are separated from the gas oil stream together with the sulfones. This operation may result in diesel yield loss therefore, the valorization or upgrade of this oxidized stream affects the process economics. This stream can be blended into the heating oil pool or treated in a hydrocracking unit to recover valuable products. 

Several research approaches and industrial developments have been attempted in order to achieve these objectives. We shall consider the chemical, textural, and mechanical properties and the thermal stability of the main alumina carriers manufactured by Rhone-Poulenc as well as the effects of adding various oxides on these properties and on the performance of oxide-based catalysts. 

Maintaining the concentration of the active phase constant (Cu and Ni), two further oxide based catalysts were prepared using as supports sepiolite "STCuNi" and a mixture of sepiolite and alumina "SACuNi" respectively. These were compared with the catalyst described previously "SLCuNi" prepared on a support of sepiolite which had been washed with an acid solution. 

The metal oxide based catalysts, i.e. the un-impregnated washcoats, are also forming metal sulfates and sulfites with the SO2 [13, 19]. These compounds are generally less stable at the high temperature, which is required for the CH4 combustion, and hence they were not affected by the SO2. For the H2 and CO their ignition temperatures are well within the stability range for the metal sulfates, and they were also affected. In the case of YAG the effect was an improvement of the catalytic activity, however small, this could probably be contributed to the increased acidity of the catalysts, as have been described for alumina catalysts. 

Preparations based on molybdenum oxide are called Standard Oil Co. catalysts, while those based on chromium oxide are known as the Phillips Petroleum Co. catalysts. Below is a description of a preparation of a molybdenum-based catalyst. Alumina is saturated with a solution of anunonium molybdate and then subjected to heating in air at 500 to 600 °C. The oxide that forms is reduced with hydrogen at 430 to 480 °C. Reducing agents like CO, SO, or hydrocarbons are also used. Hydrogen, however, is preferred at pressures of approximately 75 psi. The catalyst may contain between 5 and 25% of the molybdenum compound dispersed on the surface. " ... 

Generally, there are two possibilities how to use mesoporous molecular sieves as supports for metathesis catalysts. First, to apply them as supports for heterogeneous metal oxide-based catalysts instead of classical silica or alumina. Second, to use them for preparation of heterogenized versions of originally homogeneous metathesis catalysts, especially for anchoring well-defined carbene complexes. 

Early reports on this reaction were focused on iron oxide-based catalysts, supported on different supports alumina, zeolite, and active carbon, among others. Later, hydrotalcite-like compounds, and the topical V-Mg-0 catalysts were explored. Park and his group, one of the most active in this field, first reported the use of zirconia as a catalyst, " and later on that of ceria-zirconia-based catalysts and vanadium-antimony oxide-based catalysts. Publications up to 2007 have been subject of several reviews. Therefore, the most relevant feamres will be revised hereinafter, as well as more recent publications, and the reader is invited to get further details in the aforementioned reviews. 

Processes rendered obsolete by the propylene ammoxidation process (51) include the ethylene cyanohydrin process (52—54) practiced commercially by American Cyanamid and Union Carbide in the United States and by I. G. Farben in Germany. The process involved the production of ethylene cyanohydrin by the base-cataly2ed addition of HCN to ethylene oxide in the liquid phase at about 60°C. A typical base catalyst used in this step was diethylamine. This was followed by liquid-phase or vapor-phase dehydration of the cyanohydrin. The Hquid-phase dehydration was performed at about 200°C using alkah metal or alkaline earth metal salts of organic acids, primarily formates and magnesium carbonate. Vapor-phase dehydration was accomphshed over alumina at about 250°C. 

Benzene-Based Catalyst Technology. The catalyst used for the conversion of ben2ene to maleic anhydride consists of supported vanadium oxide [11099-11-9]. The support is an inert oxide such as kieselguhr, alumina [1344-28-17, or sUica, and is of low surface area (142). Supports with higher surface area adversely affect conversion of benzene to maleic anhydride. The conversion of benzene to maleic anhydride is a less complex oxidation than the conversion of butane, so higher catalyst selectivities are obtained. The vanadium oxide on the surface of the support is often modified with molybdenum oxides. There is approximately 70% vanadium oxide and 30% molybdenum oxide [11098-99-0] in the active phase for these fixed-bed catalysts (143). The molybdenum oxide is thought to form either a soUd solution or compound oxide with the vanadium oxide and result in a more active catalyst (142). 

Other metal oxide catalysts studied for the SCR-NH3 reaction include iron, copper, chromium and manganese oxides supported on various oxides, introduced into zeolite cavities or added to pillared-type clays. Copper catalysts and copper-nickel catalysts, in particular, show some advantages when NO—N02 mixtures are present in the feed and S02 is absent [31b], such as in the case of nitric acid plant tail emissions. The mechanism of NO reduction over copper- and manganese-based catalysts is different from that over vanadia—titania based catalysts. Scheme 1.1 reports the proposed mechanism of SCR-NH3 over Cu-alumina catalysts [31b],... 

The acid-base oxides such as aluminas were used as catalysts, adsorbents or catalyst supports and it was interesting to know the surface acid-base properties of these catalysts. 

Catalysts used for hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) of heavy oil fractions are largely based on alumina-supported molybdenum or tungsten to which cobalt or nickel is added as a promoter [11]. As the catalysts are active in the sulfided state, activation is carried out by treating the oxidic catalyst precursor in a mixture of H2S and H2 (or by exposing the catalyst to the sulfur-containing feed). The function of hydrogen is to prevent the decomposition of the relatively unstable H2S to elemental sulfur, which would otherwise accumulate on the surface of the... 

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