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4588836 
Journal Article 
Effect of varying reflux durations on the physico-chemical and catalytic performance of vanadium phosphate catalysts synthesized via vanadyl hydrogen phosphate sesquihydrate 
Leong, LK; Chin, KS; Taufiq-Yap, YH 
2012 
1 
Applied Catalysis A: General
ISSN: 0926-860X
EISSN: 1873-3875 
415 
53-58 
WOS:000301020800008 
A series of vanadyl pyrophosphate, (VO)(2)P2O7, catalysts prepared via vanadyl hydrogen phosphate sesquihydrate precursors (VOHPO4 center dot 1.5H(2)O) was calcined in a reaction flow of 0.75% n-butane in air mixture at 733 K for 18h. The precursors have been synthesized by refluxing vanadyl phosphate dihydrate (VOPO4 center dot 2H(2)O) with 1-butanol for different lengths of time, i.e. 8, 15 and 24h, and the produced catalysts were denoted as VPOs-R8, VPOs-R15 and VPOs-R24, respectively. X-ray diffraction (XRD) patterns of the three catalysts showed similar diffraction pattern, comprised of a well-crystallized (VO)(2)P2O7 phase. Brunauer-Emmett-Teller (BET) surface area measurements showed that VPOs-R24 has the highest specific surface area, i.e. 31 m(2) g(-1) followed by 27 m(2) g(-1) and 19 m(2) g(-1) for VPOs-R15 and VPOs-R8, respectively. Inductively coupled plasma (ICP) analyses indicated that the P/V atomic ratios of these catalysts were in the optimum range in producing (VO)(2)P2O7 phase. A small increment in the average oxidation number of the vanadium was observed as the precursor reflux duration increased. Scanning electron microscope showed the secondary structures of the catalysts with plate-like crystals in different sizes, which were agglomerated into rosette-shape clusters. The total amount of oxygen desorbed from the catalysts increased as the precursor reflux duration increased. Temperature-programmed reduction (TPR) in H-2 profiles of all the catalysts gave three reduction peaks. VPOs-R8 gave the highest total amount of oxygen removed from V5+/V4+ phase followed by VPOs-R15 and VPOs-R24. Catalytic tests revealed that the catalyst with lower precursor reflux duration exhibited higher selectivity but lower activity and vice versa. (C) 2011 Elsevier B.V. All rights reserved. 
Vanadyl hydrogen phosphate; sesquihydrate precursor; Vanadyl pyrophosphate; Selective oxidation; Maleic anhydride