Selective oxidation catalysts preparation

Active crystal face of vanadyl pyrophosphate for selective n-butane oxidation catalyst preparation, 157-158 catalyst weight vs. butane oxidation, 162,163/ catalytic activity, 162,1 (At catalytic reaction procedure, 158 experimental description, 157 flow rate of butane vs. butane oxidation, 162,163/ fractured SiOj-CVO PjO scanning electron micrographs, 160,161/ fractured scanning electron... 

As to the method of preparation, it was found that V-Mg oxide catalysts prepared with a Mg(OH)2 precursor that was precipitated with KOH was less selective than one prepared with a MgC03 purecursor precipitated with (NH4)2C03 (25). Interestingly, unlike the butane reaction, there was no effect of preparation on the oxidative dehydrogenation of propane using the same catalysts, as mentioned earlier (25, 30). Unlike the oxidation of propane, Mg pyrovanadate was nonselective for butane (25, 26). Mg metavanadate was nonselective as well (26). 

Daniel and Keulks (104) investigated Bi-Fe-Mo oxide catalysts prepared by reacting the a-bismuth molybdate with ferric hydroxide. Comparison of these catalysts with bismuth molybdate and ferric oxide indicated that mechanistically the Bi-Fe-Mo oxide catalysts resembled bismuth molybdate in their ability to form an allyl species. Under the same reaction conditions, the composition with Bi-Fe-Mo atomic ratio equal to 6 9 10 exhibited higher conversion than and the same selectivity as the bismuth molybdate catalysts. In contrast to bismuth molybdate, the Bi-Fe-Mo oxide catalysts were found to maintain their activity and se-... 

Moser, W. R., Hydrocarbon partial oxidation catalysts prepared by the high-temperature aerosol decomposition process, in Catalytic Selective Oxidation, ACS Symp. Ser. (S. T. Oyama and J. W. Hightower, Eds.), pp. 523,244 (1993). 

The addition of Cu to K/Fe oxides catalyst enhanced its ability of ethanol production. K/Cu-Fe oxides catalysts, prepared by kneading KjCO, with Cu-Fe co-precipitate, gave the ethanol selectivity of more than lOC-% at 300°C. The combination of K/Fe and Cu-Zn gave remarkable results on ethanol production. In the reaction over K/Cu-Zn-Fe oxides catalyst, CO2 conversion of 44% and ethanol selectivity of 20C-% were obtained under the standard reaction conditions. Besides ethanol, hydrocarbons were produced with a selectivity of almost 45C-%. The formation of hydrocarbons seems inevitable as long as Fe-based catalysts are employed. 

One other notable method has been used in the preparation of mixed transition metal molybdates, amongst many other oxide systems. This novel method(TT) involves preparation of the mixed metal oxides via an amorphous precursor such as a citrate salt of the appropriate metals, and then thermal decomposition of the complex to yield the resulting mixed oxides. The experimental procedures are described in four French patents(78-81), giving details of many different preparations including a proposed M0O3 rich, chromium doped iron molybdate, prepared as a possible selective oxidation catalyst. 

It is apparent that the two catalysts give comparable yields of the desired PA product, under comparable reaction conditions. Therefore, it is concluded that the solventless ballmilling method described herein is a viable method of preparing selective oxidation catalysts. 

In the early literature it was reported that Si02-Al203 [10,11] and supported tungsten oxide [11] had high activity and selectivity for -caprolactam. Tungsten oxide catalysts prepared from the hydrolysis of WClg and supported on silica gel were more caprolactam selective than the catalyst prepared from ammonium tungstate... 

As a major step in the evaluation of the above mentioned high-throughput tools and techniques, a scale-down of different types of catalysts for several applications was performed. For that purpose, two well established commercial catalysts, one of the mixed metal oxide type for selective olefin oxidation and one impregnated catalyst for ethylene acetoxylation to vinyl acetate monomer (VAM), respectively, were prepared in the small-scale and their catalytic performance was compared. As shown in Fig. 1 with the selective oxidation catalyst, the scale-down of this catalyst was successful, since both, the commercial and the high-throughput prepared catalyst are showing identical performances. Regarding the calcination procedure one can point out, that only if this step is carried out in the 5-fold rotary kiln, equal catalysts were obtained. 

We compare the structure of Fe(III) active sites in the small pore FeAlPO-18 and large pore FeAlPO-5 catalysts prepared using appropriate structure directing agents. The present study clearly points out that it is possible to substitute Fe(III) ions for tetrahedrally coordinated Al(IlI) in the framework of AlPO-5 and AlPO-18 to yield an active and selective oxidation catalysts. The use of atomistic simulations is again proven to provide accurate geometries which, when combined with the analysis of the EXAFS data, yield accurate models for the active sites. 

Phthalocyanine complexes within zeolites have also been prepared by the ship-in-a-bottle method (see Section 6.6), and have subsequently been investigated as selective oxidation catalysts, where their planar metal-N4 centres mimic the active sites of enzymes such as cytochrome P450, which is able to oxidize alkanes with molecular oxygen. Cobalt, iron and ruthenium phthalocyanines encapsulated within faujasitic zeolites are active for the oxidation of alkanes with oxygen sources such as iodosobenzene and hydroperoxides. Following a similar route, Balkus prepared Ru(II)-perchloro- and perfluorophthalocyanines inside zeolite X and used these composites for the selective catalytic oxidation of alkanes (tert-butylhydroperoxide). The introduction of fluorinated in place of non-fluorinated ligands increases the resistance of the complex to deactivation. 

Mn-containing dendrimers have been prepared and explored as selective oxidation catalysts [20, 21], Improved regioselectivity was observed with various alkene substrates compared to that achieved with the non-dendronized metalloporphyrin. 

Rives et al. (427,428) studied the hydrogenation of acetylene to ethylene with multimetallic oxide catalysts prepared by calcining ZnNiAlCr-LDHs at 500°C for 3 h with an H2/N2 (50 50 vol) gas mixture. The redox property of Ni is essential for the activity and selectivity of the catalysts and the presence of ZnO decreases the coke formation. 

Keywords Iron molybdate catalyst. Selective catalytic oxidation. Catalysts preparation... 

Today the most efficient catalysts are complex mixed metal oxides that consist of Bi, Mo, Fe, Ni, and/or Co, K, and either P, B, W, or Sb. Many additional combinations of metals have been patented, along with specific catalyst preparation methods. Most catalysts used commercially today are extmded neat metal oxides as opposed to supported impregnated metal oxides. Propylene conversions are generally better than 93%. Acrolein selectivities of 80 to 90% are typical. 

Ethylene Oxide Catalysts. Of all the factors that influence the utihty of the direct oxidation process for ethylene oxide, the catalyst used is of the greatest importance. It is for this reason that catalyst preparation and research have been considerable since the reaction was discovered. There are four basic components in commercial ethylene oxide catalysts the active catalyst metal the bulk support catalyst promoters that increase selectivity and/or activity and improve catalyst life and inhibitors or anticatalysts that suppress the formation of carbon dioxide and water without appreciably reducing the rate of formation of ethylene oxide (105). 

Among the J ,J -DBFOX/Ph-transition(II) metal complex catalysts examined in nitrone cydoadditions, the anhydrous J ,J -DBFOX/Ph complex catalyst prepared from Ni(C104)2 or Fe(C104)2 provided equally excellent results. For example, in the presence of 10 mol% of the anhydrous nickel(II) complex catalyst R,R-DBFOX/Ph-Ni(C104)2, which was prepared in-situ from J ,J -DBFOX/Ph ligand, NiBr2, and 2 equimolar amounts of AgC104 in dichloromethane, the reaction of 3-crotonoyl-2-oxazolidinone with N-benzylidenemethylamine N-oxide at room temperature produced the 3,4-trans-isoxazolidine (63% yield) in near perfect endo selectivity (endo/exo=99 l) and enantioselectivity in favor for the 3S,4J ,5S enantiomer (>99% ee for the endo isomer. Scheme 7.21). The copper(II) perchlorate complex showed no catalytic activity, however, whereas the ytterbium(III) triflate complex led to the formation of racemic cycloadducts. 

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