Molybdate, impregnation with

In an alternative industrial process, resorcinol [108-46-3] is autoclaved with ammonia for 2—6 h at 200—230°C under a pressurized nitrogen atmosphere, 2.2—3.5 MPa (22—35 atm). Diammonium phosphate, ammonium molybdate, ammonium sulfite, or arsenic pentoxide maybe used as a catalyst to give yields of 60—94% with 85—90% selectivity for 3-aminophenol (67,68). A vapor-phase system operating at 320°C using a siUcon dioxide catalyst impregnated with gallium sesquioxide gives a 26—31% conversion of resorcinol with a 96—99% selectivity for 3-aminophenol (69). 

Silica gel G impregnated with 0.3-M aqueous sodium molybdate Silica gel G... 

Association of molybdates (tungstates) with phosphate-like structures leads to a class of compounds called heteropoly compounds or heteropoly acids of Mo or W, hereafter schematically written as Mo —P or W—P heteropoly compounds. The heteropoly anions, which may contain Mo, W, P, and other elements, are paired, both in the solid state and in solution, with cations such as H+, NH4, and Na+. Here, only some Mo —P heteropoly compounds playing an important role in hydrotreating catalysts during the catalyst preparation (impregnation) or as supported oxidic phases are discussed. The Mo — P heteropoly compounds have the following properties 18,19) ... 

Metal oxides on zeolites have also found use as redox catalysts. High-temperature (700-750 °C) dehydroaromatization of methane under nonoxidizing conditions has been explored with a number of zeolitic catalysts modified with transition metal ions. Although coke formation at these high temperatures is a problem, calcined molybdate-impregnated ZSM-5 shows unparalleled activity of up to 8 % methane conversion with 100 % selectivity towards aromatics. Surface studies of these Mo HZSM-5 catalysts indicate that M0O3 crystals are on the external zeolite surface [123]. 

A detailed description of a chromia-on-alumina catalyst prepared by impregnation has been given elsewhere . Another supported nonmetallic catalyst widely used commercially is cobalt molybdate-on-alumina. The preparation of this catalyst using an alumina support with controlled pore-size distribution is as follows. Silica-stabilized alumina, with greater than 50% of its surface area in 3-8 nm pores and at least 3% of the total pore volume in pores greater than 200 nm in diameter, is impregnated with an aqueous solution of cobalt and molybdenum. The finished oxysulfide catalyst was tested for hydrodesulfurization of petroleum residuum at 370°C and 100 atm for 28 days and compared with a convential cobalt-molybdate catalyst having a major portion of the surface area in 3-7 nm pores. The latter catalyst and controlled pore catalyst maintained 57 and 80% activity, respectively. 

Deposition of molybdenum(III)oxide onto a silica support was reahzed at pH = 8.7 at temperatures of 0-60 °C over a wide range of loadings of 1-20 wt% Mo. As can be inferred from Equation 6.7 it is to be expected that a lower pH will favor this redox reaction. Based on this fact a very peculiar phenomenon was noted and exploited. Using silica spheres of 1.5 mm size an impregnation with the aqueous molybdate/hydrazine solution was carried out. It was observed that under certain conditions of concentrations and temperature the deposition of the (brown) Mo compound took place... 

Si-CT and Al-CT after calcination at 723 K were used as supports for Mo and Ni. Catalytic activities were evaluated by using hydrogenation of pyrene. Mo was loaded into Si-CT by impregnation with an aqueous solution of ammonium molybdate(VI) tetrahydrate, and Ni from nickel(II) nitrate hexahydrate was then loaded by impregnation. The NiMo catalysts... 

Srivastava and co-workers (125) separated 30 synthetic dyes on silica gel plates impregnated with ammonium molybdate and copper sulfate using BUOH-ACOH-H2O (25 5 10) and BuOH-50% NH3-dioxane (25 5 10) as mobile phases. No tailing of spots was observed on ammonium molybdate-and copper sulfate-impregnated plates using the above mobile phases. The data on h7 y values are recorded in Table 11. The h/ y values were not altered when dye mixtures were applied. 

Procedure. A small filter paper is impregnated with nitric acid-molybdate solution. The mounted section or the polished area of the rock is warmed (the section should not be heated to the point that the Canada balsam becomes mobile) and pressed at once on the moist paper and left for 1 or 2 minutes. The paper is laid (with the surface of contact upward) on a second paper soaked in benzidine solution, so that the solution rises through the upper paper. The latter is then held over ammonia and an exact blue print is obtained of the crystals of apatite in the section. If the contours of the section have been drawn on the paper, the exact location of the crystals is revealed. Even the smallest crystals of apatite, of whose apatitic nature there may be some doubt, may be identified in this way, thus amplifying or even replacing optical examination. 

In 1975, Ohloff etal. studied the gas-phase oxidation of ot-isophorone to KIP over a vanadia/pumice catalyst modified with 1 wt% of hthium phosphate at 230°C. Under these conditions, simultaneous formation of KIP and formylisophorone occurred. More than 20 years later, Baiker et al. revisited the catalytic gas-phase oxidation of isophorone. At 200-250°C, 75% combined yields of KIP and formyhsophorone were obtained at 17% ot-isophorone conversion over vanadia/pumice impregnated with hthium phosphate j6-isophorone was found as a major by-product (18%). Bismuth molybdate or vanadium phosphate showed poor selectivity and rapid deactivation. The Ag/y-alumina-catalysed oxidation was unselec-tive and resulted mainly in isomerisation to j6-isophorone. Chromia-based catalysts led to an increased formation of 3,5-xylenol. To efficiently remove coke deposits and to re-oxidise vanadium oxides to vanacha, temperatures higher than 300°C would be needed however, under these conditions isophorone and KIP are not stable. Thus, highly selective catalysts would be required which are active at lower temperatures. 

Phosphatides in lecithin Merck Silica Gel 60, impregnated with H3PO4 65 25 4.3 CHCl3/MeOH/0.2 M acetate buffer, pH 4 Molybdic acid reagent 82... 

The catalysts are prepared by impregnating the support with aqueous salts of molybdenum and the promoter. In acidic solutions, molybdate ions are present largely in the form of heptamers, [Mo2024] , and the resulting surface species are beHeved to be present in islands, perhaps containing only seven Mo ions (100). Before use, the catalyst is treated with H2 and some sulfur-containing compounds, and the surface oxides are converted into the sulfides that are the catalyticaHy active species. 

Figure 8.12 Raman spectra of alumina- and silica-supported molybdena catalysts after impregnation of the supports with solutions of ammonium heptamolybdate, (NH4)6Mo7024 4 H20 of different pH values, and after calcination in air at 775 K. See Table 8.3 for a list of characteristic Raman frequencies of molybdate species. The sharp peaks in the spectra of the calcined MoOySiOj catalyst are those of crystalline Mo03 (from Kim el at. [43J).

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