Sustainable Acrylic Acid Making via Acetic Acid–Formaldehyde Condensation: The Highly Selective and Durable VPO-TiO<sub>2</sub> Catalyst Accomplished by VPO Phase Control and Wet Co-Mechanical Milling
Jun Liu, Pengcheng Wang, Peiwen Xu, Zhijia Xu, Xinzhen Feng, Weijie Ji, Hamidreza Arandiyan, Chak‐Tong Au
Abstract
On the basis of the precise phase control of vanadium phosphorus oxides (VPOs), nanosized TiO2 was employed as a dopant/dispersant to fabricate a series of VPO-TiO2 catalysts through a wet mechanical co-milling process. The resulting catalysts showed outstanding durability plus excellent target products [acrylic acid (AA) + methyl acrylate (MA)] selectivity via acetic acid (HAc)–formaldehyde (FA) condensation. Over an optimized catalyst of 20% VPO-TiO2, the (AA + MA) selectivity being 85% (HAc input-based) at a yield level >60% (FA input-based) can be achieved after 180-h running, the best known to date over the VPO-based catalysts. The detailed characterizations including X-ray powder diffraction, Raman spectra, XPS, and H2-TPR indicated that the V5+ in the original VOPO4 phase would be partially reduced in the presence of TiO2 after the milling process in the cyclohexane medium; and the partially reduced VOPO4 phase together with the decorated TiO2 component stabilized the remaining V5+ entities and considerably slowed down the continuous reduction of surface V5+ species, accounting for substantially enhanced catalyst durability as well as target product selectivity. The NH3-/CO2-TPD results demonstrated that the surface acid–base property also varied notably with the VPO content which in turn controlled the HAc conversion and (MA + AA) selectivity accordingly.