7Ai M, Fujihashi H. Production of methacrylic acid by vapor-phase aldol condensation of propionic acid with formaldehyde over silica-supported metal phosphate catalysts[ J]. Applied Catalysis A, 2003, 252 (1) :185-191.
8Ai M. Vapor-phase aldol condensation of formaldehyde with acetic acid on V205-P205 catalysts[ J]. Journal of Catalysis, 1987, 107 ( 1 ) :201-208.
9Ai M. Vapor-phase aldol condensation of formaldehyde with propionic acid on Vanadium Pentoxide-Phosphorus [ J ]. Applied Catalysis, 1988, 36:221-230.
10Wolfgang Gerhartz. Ullmann' s Encyclopedia of Industrial Chemistry [M]. Federal Republic of Germany, 1987.