Abstract: A method for the production of p-methoxybenzaldehyde by the vapor-phase catalytic oxidation of p-methoxytoluene, which method comprises cooling and condensing a mixed gas formed by said reaction of oxidation thereby preparing a solution containing p-methoxybenzaldehyde, treating said solution in the presence of at least one alkali selected from the group consisting of an alkali metal compound and an ammonium compound soluble in water and alkaline in nature, and subsequently distilling the resultant treated solution.

Abstract: A catalyst for manufacturing methacrolein by the vapor phase oxidation of isobutylene or tertiary butanol, said catalyst having the composition represented by the following formulaMo.sub.a W.sub.b Bi.sub.c Fe.sub.d A.sub.e B.sub.f C.sub.g D.sub.h O.sub.xwhereinA represents at least one element selected from the group consisting of nickel and cobalt,B represents at least one element selected from the group consisting of alkali metals, alkaline earth metals and thallium,C represents at least one element selected from the group consisting of tellurium, antimony, tin, cerium, lead, manganese and zinc,D represents at least one element selected from the group consisting of silicon, aluminum, zirconium and titanium,a, b, c, d, e, f, g, h, and x respectively represent the atomic ratios of Mo, W, Bi, Fe, A, B, C, D, and O, and whena is fixed at 12,b is from 0 to 10,c is from 0.1 to 10,d is from 0.