Sustainable Acrylic Acid Making via Acetic Acid–Formaldehyde Condensation: The Highly Selective and Durable VPO-TiO2 Catalyst Accomplished by VPO Phase Control and Wet Co-Mechanical Milling

• Published in: ACS sustainable chemistry & engineering Vol. 8; no. 49; pp. 18034 - 18043
• Main Authors: Liu, Jun, Wang, Pengcheng, Xu, Peiwen, Xu, Zhijia, Feng, Xinzhen, Ji, Weijie, Arandiyan, Hamidreza, Au, Chak-Tong
• Format: Journal Article
• Language: English
• Published: American Chemical Society 14.12.2020
• Subjects: Mechanical ball-milling; Acrylic acid; Vanadium phosphorus oxide; Acetic acid; Condensation; Formaldehyde; TiO2
• ISSN: 2168-0485; 2168-0485
• DOI: 10.1021/acssuschemeng.0c05916

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.