Sulfate-supported metal oxides preparation

Solid catalysts can be used at elevated temperatures, though their acidities are much weaker than those of liquid ones. From this point of view, solid superacids based on Lewis acids and liquid superacids discussed in Sections II—1V are not sufficiently stable Nafion-H is also unsatisfactory, its maximum operating temperature being below 200°C. A new type of the sulfate-supported metal oxides is more stable because of preparatory heat treatment at high temperatures, but elimination of the sulfate is sometimes observed during reaction, thus it is hoped to synthesize superacids with the system of metal oxides. Another type of superacid, tungsten or molybdenum oxide supported on zirconia, has been prepared by a new preparation method, and its stability is satisfactory so far. It is hoped that the preparation method will be extensively applied to other metal oxides for new solid superacids. 

The formation of Fe2(S04)3 can also be prohibited by the use of other metal oxides. Because molybdenum sulfates are not known, iron-molybdenum mixed oxide absorbents were prepared and tested. Figure 7 shows a H2S absorption curve of P5/2Fel2MolO. The capacity is slightly smaller than observed with iron-molybdenum mixed oxide absorbents supported by silica due to the strong interaction of a part of the active compounds with the phosphate groups. The metal phosphates formed are not active in the absorption of H2S. 

The most active catalysts for many tritiolyses are palladium metal (freshly prepared from PdO) or palladium supported on charcoal, barium sulfate or aluminum oxide, but palladium catalysts are sometimes associated with side reactions such as O- and /V-debenzylations, isomerizations and labeling of certain sites by catalytic exchange (see Chapter 3, Section 3.3). For example, in the case of [ H]papaverine (10 and the [ H]pargyline precursor... 

The presence of thallium(0) led to an increase in activity and selectivity of metallic palladium catalysts supported on silica in aldose oxidation reactions. However, silica-supported thallium(0) had no activity by itself (entry 3). ° Similarly, the bimetallic catalyst platinum-thallium/ZSM-5, prepared by impregnation of thallium sulfate and chloroplatinic acid on Zeolite Socony Mobil-5 (ZSM-5), showed greater selectivity in propane aromatisation and almost the same catalytic activity as monometallic thallium/ZSM-5 (entry 4). Similar comparison of vanadium-caesium-copper and vanadium-caesium-copper-thallium catalysts supported on TiOa.SiC demonstrated that addition of thallium improved the catalytic activity in partial oxidation of p-tert-butyltoluene to p-tert-butyl-benzaldehyde (entry The application of solid-supported thallium-based catalysts in different processes includes (a) iron-thallium catalysts in carbon monoxide hydrogenations to form hydrocarbons and alcohols, and catalytic reforming of... 

Transition metal-catalyzed routes are also known for the conversion of arylboronic acids into phenols. Of the copper-catalyzed approaches, the methods that are tolerant to air and water are particularly practical due to the operational simplicity. One example of this chemistry entailed the use of copper sulfate as the catalyst (Scheme 2.34 and Example 2.5) [44]. Using 1,10-phenanthroline as a supporting ligand for the copper center, a wide array of electron-deficient and electron-rich arylboronic acids were converted into phenols in excellent yields. Even bulky arylboronic acids such as 2,6-dimethylphenylboronic acid were successfully converted (87%). In related work, copper oxide has also been successfully used to prepare phenols in water and under air from arylboronic acids bearing an assortment of electron-donating and electron-withdrawing groups (Schane 2.35) [45]. 

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