Nh4vo3

Na₂MoO₄·2H₂O and Na₂SiO₄·2H₂O were purchased from Tianjin Chemical Reagent No.4 Factory (Tianjin, China). NH₄VO₃ was purchased from Tianjin Guangfu Fine Chemical Research Institute (Tianjin, China). The 1,4-Dioxane (C₄H₈O₂) was purchased from Tianjin Guangcheng Chemical Reagent Co., Ltd. (Tianjin, China). Tetra-n-Butylammonium Bromide (n-Bu₄NBr) and Dichloromethane (CH₂Cl₂) were purchased from Tianjin Fuchen Chemical Reagent Factory (Tianjin, China). Phosphoric acid (H₃PO₄, 85%) was purchased from Laiyang Kangde Chemical Co., Ltd. (Shandong, China). Sodium bicarbonate (NaHCO₃) was purchased from Tianjin Denke Chemical Reagent Co., Ltd. (Tianjin, China). Morpholine ethyl sulfonic acid was purchased from Maclean biochemical Co., Ltd. (Shanghai, China). The 1-Butyl-3-methylimidazole chloride ([Bmim]Cl) and 1-Butyl-3-methylimidazole acetate ([Bmim]OAc) were purchased from Shanghai Chengjie Chemical Co., Ltd. (Shanghai, China). Ether was purchased from Sinopharm Chemical Reagent (Shanghai, China). The reagents were all analytically pure. All chemicals were used as received.

The VO_x-CeO₂ catalysts were prepared via two-step-impregnation procedure by dissolving Ce(NO₃)₄.6H₂O (99.5%, Aladdin (China) Chemical Co., Ltd) in deionized water (2 mL/g Al₂O₃) with γ-Al₂O₃ (Adamas, 99.99%, S_BET = 180 m²/g) as support to well disperse the cerium oxides. Then VO_x was impregnated by dissolving NH₄VO₃ (99.0%, Tianjin Guangfu Technology Development Co. Ltd.) and oxalic acid (99.0%, Aladdin Industrial Corporation) [NH₄VO₃/oxalic acid = 0.5 (mole ratio)] in deionized water. The samples were dried at 80 ^oC for 12 h and then calcinated at 600 ^oC for 3 h. The VO_x-CeO₂ samples were named xV/yCeAl, where x(y) is the percent weight ratio of V(Ce). The vanadia and ceria catalysts were obtained by VO_x, and CeO₂ supported on γ-Al₂O₃ with the same V and Ce loadings with VO_x-CeO₂, respectively, as reference samples. An industrially relevant K–CrO_x/Al₂O₃ catalyst was carried out (mimic Catofin from Lummus) to compare the VO_x-CeO₂ catalyst. For K-CrO_x/Al₂O₃ reference catalysts, 20 wt% Cr and 1.0 wt% K were utilized with Cr(NO₃)₃·9H₂O (99.5%, Aladdin (China) Chemical Co., Ltd)³⁷ . The catalysts were dried for 2 h at 60 °C and overnight at 120 °C, followed by calcination at 600 °C for 3 h. The amount of Cr and K was about 19.8 wt% and 0.98 wt% based on the weight ratio of M to Al₂O₃, which were determined by inductively coupled plasma optical emission spectroscopy (ICP-OES),