CATALYSIS BY HETEROPOLY COMPOUNDS .17. FACTORS CONTROLLING THE SELECTIVITY OF THE OXIDATION OF ACETALDEHYDE OVER HETEROPOLY COMPOUNDS

The catalytic oxidation of acetaldehyde over various heteropoly compounds (alkali salts of 12-molybdophosphoric acid) was investigated in relation to the redox and acidic properties of the heteropoly compounds based on the reaction scheme proposed: {A figure is presented} where ri,'s (i = 1-5) and ki's are the rates and rate constants of respective steps, respectively. It was found that r1 (or k1), r2 (k2), and r4 (k4) were primarily determined by the oxidizing ability of catalysts measured by the rate of the reduction of the catalysts by CO and r5 (k5) was very small. On the other hand, r3 (k3) was mainly controlled by the acidic property of the catalyst (the amount of Brønsted acid site measured by pyridine uptake). The present results suggest that the heteropoly compounds having high oxidizing abilities and low Brønsted acidity are desirable for obtaining high yield of acetic acid. © 1991.