Nickel, catalyst vanadate

Under FCCU operating conditions, almost 100% of the metal contaminants in the feed (such as nickel, vanadium, iron and copper porphyrins) are decomposed and deposited on the catalyst (2). The most harmful of these contaminants are vanadium and nickel. The deleterious effect of the deposited vanadium on catalyst performance and the manner in which vanadium is deposited on the cracking catalyst differ from those of nickel. The effect of vanadium on the catalyst performance is primarily a decrease in catalyst activity while the major effect of nickel is a selectivity change reflected in increased coke and gas yields (3). Recent laboratory studies (3-6) show that nickel distributes homogeneously over the catalyst surface while vanadium preferentially deposits on and reacts destructively with the zeolite. A mechanism for vanadium poisoning involving volatile vanadic acid as the... 

Mixtures of acetaldehyde and acetic acid may be obtained121 by passing acetylene (2 to 3 volumes) and air (10 volumes) mixed with a large excess of steam over the zinc, copper, nickel, or cadmium salts of vanadic, molybdic, or chromic acids deposited upon a suitable base, such as pumice, at temperatures ranging from 300° to 400° C. For example, yields of 75 to 80 per cent acetaldehyde along with 5 per cent acetic acid have been obtained by using basic zinc vanadate at 380° C. The aldehyde is separated by fractional condensation in a column and the condensed fraction which is poor in aldehyde is utilized to furnish steam for the catalytic treatment of more acetylene. The fractions rich in acetaldehyde serve for the direct recovery of the aldehyde or may be oxidized immediately to acetic acid by passage over a suitable catalyst. In this way, the process may also be applied directly to the preparation of acetic acid from acetylene. 

The significant difference between the TOP and selectivity of bulk metal molybdates and vanadates compared with pure metal oxides was a key factor in uncovering the true surface composition of those bulk catalysts. Table 11.3 and Table 11.4 show the number of surface active sites, redox TOP, and selectivity toward methanol selective oxidation products of bulk metal vanadates and the corresponding metal oxide, respectively. Similar results were obtained for bulk metal molybdates. Bulk metal vanadates possess a high selectivity to formaldehyde with some selectivity to dimethoxy methane (nickel vanadate), dimethyl ether (niobium, chromium, and aluminum vanadates), methyl formate (magnesium, chromium, and copper vanadates), and CO2 (niobium and silver vanadates). 

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