Oxidation catalysts precursors

Figure Bl.25.9(a) shows the positive SIMS spectrum of a silica-supported zirconium oxide catalyst precursor, freshly prepared by a condensation reaction between zirconium ethoxide and the hydroxyl groups of the support [17]. Note the simultaneous occurrence of single ions (Ff, Si, Zr and molecular ions (SiO, SiOFf, ZrO, ZrOFf, ZrtK. Also, the isotope pattern of zirconium is clearly visible. Isotopes are important in the identification of peaks, because all peak intensity ratios must agree with the natural abundance. In addition to the peaks expected from zirconia on silica mounted on an indium foil, the spectrum in figure Bl. 25.9(a)...

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... 

A. Structure of the Catalyst 1. Structure of the Oxidic Catalyst Precursor... 

Girgsdies F, Schlogl R, Trunschke A. In-situ X-ray diffraction study of phase crystallization from an amorphous MoVTeNb oxide catalyst precursor. Catalysis Communications. 2012 18(0) 60-62. 

Venable, Margaret Hamm, Syntheses, structures and supported interactions of potential metal oxide catalyst precursors , MS thesis, Georgia Institute of Technology, (1990). 

The details of the preparation of the iron oxide catalyst precursors are described elsewhere [15-17], For those carbides made by exsitu carburization, the oxide was loaded into a 1 diameter quartz tube and heated in a 1/1 H2/CO mixture at a space velocity of 10,000 v/v/hr at 350°C for 24 hours. Iron carbide catalysts were also prepared by laser pyrolysis of iron carbonyl and ethylene using a 150 watt continuous wave CO2 laser to provide both a rapid high temperature reaction (, 1 sec with T 1000°C) and quench [18],... 

Mazzoni, G., Cavani, F., and Stefani, G. (1997) Process for the tranformation of a vana-dium/Phosphorous Mixed Oxide catalyst precursor into the active catalyst for the production of maleic anhydride, EP0804963B1 (assigned to Lonza). 

Less activated substrates such as uorohaloben2enes also undergo nucleophilic displacement and thereby permit entry to other useful compounds. Bromine is preferentially displaced in -bromofluoroben2ene [460-00-4] by hydroxyl ion under the following conditions calcium hydroxide, water, cuprous oxide catalyst, 250°C, 3.46 MPa (500 psi), to give -fluorophenol [371-41-5] in 79% yield (162,163). This product is a key precursor to sorbinil, an en2yme inhibitor (aldose reductase). 

Promoters are sometimes added to the vanadium phosphoms oxide (VPO) catalyst during synthesis (129,130) to increase its overall activity and/or selectivity. Promoters may be added during formation of the catalyst precursor (VOHPO O.5H2O), or impregnated onto the surface of the precursor before transformation into its activated phase. They ate thought to play a twofold stmctural role in the catalyst (130). First, promoters facilitate transformation of the catalyst precursor into the desired vanadium phosphoms oxide active phase, while decreasing the amount of nonselective VPO phases in the catalyst. The second role of promoters is to participate in formation of a soHd solution which controls the activity of the catalyst. 

In addition to rhodium(III) oxide, cobalt(II) acetylacetonate or dicobalt octacarbonyl has been used by the submitters as catalyst precursors for the hydroformylation of cyclohexene. The results are given in Table I. 

Fig. 1(b) represents the selectivity to styrene as a ftmcfion of time fijr the above catal ts. It is observed that the selectivity to styrene is more than 95% over carbon nauofiber supported iron oxide catalyst compared with about 90% for the oxidized carbon nanofiber. It can be observed that there is an increase in selectivity to styrene and a decrease in selectivity to benzene with time on stream until 40 min. In particrdar, when the carbon nanofiber which has been treated in 4M HCl solution for three days is directly us as support to deposit the iron-precursor, the resulting catalyst shows a significantly lows selectivity to styrene, about 70%, in contrast to more than 95% on the similar catalyst using oxidized carbon nanofiber. The doping of the alkali or alkali metal on Fe/CNF did not improve the steady-state selectivity to styrene, but shortened the time to reach the steady-state selectivity. 

Filling the pores of the support with a solution of the catalytically active element, after which the solvent is removed by drying, is a straightforward way to load a support with active material. However, in this process various interactions are possible between the dissolved catalyst precursor and the surface of the support, which can be used to obtain a good dispersion of the active component over the support. To appreciate the importance of such interactions we need to take a closer look at the surface chemistry of hydroxylated oxides in solution. 

To an extent the surface charges are determined by the pH of the solution, and by the isoelectric point of the oxide, i.e. the pH at which the oxide surface is neutral. The surface is negative at pH values below the isoelectric point and positive above it. Obviously, the charged state of the surface enables one to bind catalyst precursors of opposite charge to the ionic sites of the support. 

Microanalysis of a Copper-Zinc Oxide Methanol Synthesis Catalyst Precursor... 

V (2 ), Cr ( ), Zr (1 ), or Ta (1 ). The role of these promoters in the air cathode is unclear, and some have suggested that the active catalysts are alloys of the Ft with the transition metal (1,4) which form during heat-treatment of the oxide impregnated precursor. In the first section of this paper, we review the work from the Lawrence Berkeley Laboratory on the study of the mechanism of promotion of air cathode performance by these transition metal additives. 

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