A method for producing propylene, the method contains: producing a silica composite by preparing a raw material mixture containing silica and zeolite; drying the raw material mixture to obtain a dried product; and calcining the dried product; wherein the method contains the step of bringing a solution of phosphate into contact with the zeolite and/or the dried product to thereby adjust a phosphorus content in the silica composite to 0.01 to 1.0% by mass based on the total mass of the silica composite, a source of the phosphorus is phosphate, and the zeolite is of MFI type and has a SiO.sub.2/Al.sub.2O.sub.3 ratio (by mol) of 20 or more; and bringing the silica composite into contact with a hydrocarbon source containing at least one component selected from the group consisting of ethylene, ethanol, methanol, and dimethyl ether in the presence of steam.

A process for preparing acrylic acid, comprising (i) providing a stream S4 comprising a formaldehyde source and acetic acid; (ii) contacting stream S4 with an aldol condensation catalyst comprising a zeolitic material comprising aluminum in the framework structure to obtain a stream S6 comprising acrylic acid, the framework structure of the zeolitic material in (ii) comprising YO.sub.2 and Al.sub.2O.sub.3, and Y being a tetravalent element; where the total content of alkali metal and alkaline earth metal in the zeolitic material in (ii), calculated as alkali metal oxide and alkaline earth metal oxide, is from 0% to 0.1% by weight, based in each case on the total weight of the zeolitic material, and where the aldol condensation catalyst in (ii) comprises, outside the framework structure of the zeolitic material present therein, from 0% to 1% by weight of vanadium, based on vanadium as vanadium(V) oxide.