Industrial-scale catalytic gas phase oxidation reaction generally uses a fixed-bed reactor in which a starting compound-containing gas is made to pass through a reaction tube filled with catalyst and is thus allowed, to react. In particular for the production of (meth)acrolein and (meth)acrylic acid by catalytic gas-phase oxidation reaction of propylene, propane, isobutylene, etc., as a raw material compound, there has widely been employed a catalytic gas-phase oxidation reaction with a fixed bed multitubular reactor which is filled with solid particulate heterogeneous catalyst. Solid particulate heterogeneous catalyst which is to be used for this purpose generally includes a molded catalyst (unsupported catalyst) which is composed of active ingredients which have been molded into a specific geometric shape and a supported catalyst which is composed of a carrier material which has a geometric shape like that of molded catalyst and which has been coated with active ingredients (Patent Document 1).
Most popular for producing acrylic acid with a fixed-bed multitubular reactor which is filled with solid particulate heterogeneous catalyst is a method of two-step catalytic gas-phase oxidation by which acrolein is mainly obtained by catalytic gas-phase oxidation of propylene, and, then, acrylic acid is obtained by catalytic gas-phase oxidation of thus obtained acrolein. Also for the second step reaction of producing acrylic acid by the oxidation of acrolein, there have been proposed various methods for producing acrylic acid with a high yield. Most of such proposals relate to molybdenum-vanadium catalysts each of which mainly comprises molybdenum and vanadium which are used in the above-mentioned reaction, in detail to the composition, shape, physical properties of the catalysts and how to produce the same (Patent Documents 2, 3, and the like). There have also been made some proposals which relate to how to fill reaction tubes of a fixed-bed multitubular reactor with catalyst (Patent Documents 4, 5 and 6).