A type of precisely phase-modulated vanadium phosphorus oxides (VPOs) was fabricated for the first time by quantitatively mixing the pure phase of gamma-VOPO4 , delta-VOPO4, and (VO)(2)P2O7 in certain ratios through a mechanical milling approach. The resulting materials were used as catalysts for very efficient condensation of acetic acid and formaldehyde to acrylic acid as well as methyl acrylate. The modulated dual phase VPO catalyst outperforms the single-phase counterpart, and by optimizing the reaction conditions especially the contact time, we can further considerably enhance the catalyst performance. Over an optimized catalyst of delta-VOPO4 /gamma-VOPO4 (w/w, 3/1), the (AA + MA) yield of 84.2% with the equivalent (M + MA) formation rate of 1.71 mmol.g(-1).h(-1) or the (AA + MA) yield of 41.8% with the equivalent (AA + MA) formation rate of 4.25 mmol.g(-1).h(-1) is achievable at 360 degrees C on the formaldehyde input basis. This sort of catalyst is rather durable within a period of 110 h, and fully recovered by simple air-treatment at the reaction temperature. Due to the enhanced conjunction at the interface of two phases, the surface property of phase-modulated catalyst such as the P-O bond length and surface acidity is notably modified/enhanced, accounting for the promising catalytic performance. (C) 2019 Elsevier Inc. All rights reserved.