Solvothermal synthesis of vanadium phosphate catalysts for n-butane oxidation

Abstract

a b s t r a c tIn this paper, we have developed a simple, low-cost, template-free and surfactant-free solvothermal process for synthesis of vanadyl hydrogen phosphate hemihydrate (VOHPO 4 ·0.5H 2 O) with well defined crystal size. The synthesis was performed by reaction of VPO 4 ·2H 2 O with an aliphatic alcohol (isobutyl alcohol, 1-pentanol, 1-hexanol, 1-heptanol or 1-decanol). This afforded well crystallized VOHPO 4 ·0.5H 2 O by solvothermal methods at 120 • C temperature. This new method significantly reduced the preparation time and lowered production temperature (50%) of catalyst precursor (VOHPO 4 ·0.5H 2 O) when compared to conventional hydrothermal synthesis methods. By varying the reducing agent, the solvothermal evolution process from layered tetragonal phase VOPO 4 ·2H 2 O to orthorhombic phase VOHPO 4 ·0.5H 2 O was observed. It was found that the length of carbon chain in an alcohol in the solvothermal condition had a great impact on chemical and physical properties of resulting catalysts. Interestingly, there was no trace of VO(H 2 PO 4 ) 2 an impurity noted to be readily formed under solvothermal preparation condition. Therefore, this study introduces a more facile synthetic pathway to V(III) compounds. In addition, the microwave-synthesized catalysts exhibited some properties superior to those of conventionally synthesized catalyst such as better stability, crystallinity, and catalytic activity in the production of maleic anhydride. The characterization of both precursors and calcined catalysts was carried out using X-ray diffraction (XRD), inductively coupled plasma-atomic emission spectrometer (ICP-AES), N 2 physisorption, temperature programmed reduction (H 2 -TPR) and scanning electron microscopy (SEM). The XRD pattern of the active catalyst prepared by this solvothermal method confirmed the presence of smaller crystal size (between 6 and 13 nm along 0 2 0 planes) of vanadium phosphate catalyst with higher specific surface area. Finally, the yield of maleic anhydride was significantly increased from 29% for conventional catalyst to 44% for the new solvothermal catalyst.Crown

Innovative process for the synthesis of vanadyl pyrophosphate as a highly selective catalyst for n-butane oxidation

“…The alcohol plays a role in establishing the morphology of the vanadyl hydrogen phosphate hydrate which, since the transformation to the final catalyst is topotactic, controls the morphology of the final catalyst [8]. We have recently reported a high-pressure solvothermal process to synthesise high crystalline catalyst precursor, VOHPO 4 ·0.5H 2 O [11,14]. It was found that the alcohol used as a reducing agent can control the morphology and the best results are obtained using primary alcohols.…”

“…Initial catalyst preparations [9] used water as solvent but most studies, in recent years, have concentrated on the use of alcohols as they can exhibit the duel role of solvent and reducing agent. In previous studies [10][11][12][13] we have shown that very active catalysts can be prepared using an organic (VPO) and dihydrate (VPD) method. The alcohol plays a role in establishing the morphology of the vanadyl hydrogen phosphate hydrate which, since the transformation to the final catalyst is topotactic, controls the morphology of the final catalyst [8].…”

Synthesis, Characterization and Electrochemical Evaluation of Layered Vanadium Phosphates as Cathode Material for Aqueous Rechargeable Zn-ion Batteries

“…In addition, several more of the indexed peaks matched that of oxovanadium phosphate dihydrate from the database (ICDD:98-020-0884) (Tietze, 1981). However, the peak with the highest intensity at 2θ = 12.3 • corresponds to V 2 O 5 phase (Rownaghi et al, 2009). Peaks of significant intensity that corresponds to VOPO 4 and VOHPO 4 .2H 2 O were identified in the XRD pattern of VOP2.…”

Transition metal oxide (NiO, CuO, ZnO)-doped calcium oxide catalysts derived from eggshells for the transesterification of refined waste cooking oil

“…The crystallite size was inversely proportional to the BET surface area, in which a large crystallite size could reduce the surface area of the catalyst. 26 Moreover, the CuO/CaO(10 : 90)(ES) catalyst calcined at 700 C recorded the highest crystallite size of CaO (55.24 nm), CuO (41.91 nm) and CaCuO 2 (41.81 nm), followed by the crystallite size of the ZnO/CaO(10 : 90)(ES) catalyst calcined at Overall, the micrographs showed an irregular shape with varied particle size on the surface of the catalysts. Based on the FESEM micrograph in Fig.…”