Preparation of Vanadium Phosphate Catalysts from VOPO 4  2H 2 O: Effect of Microwave Irradiation on Morphology and Catalytic Property Y. H. Taufiq-Yap Æ A. A. Rownaghi Æ M. Z. Hussein Æ R. Irmawati Received: 19 March 2007 / Accepted: 26 June 2007 / Published online: 20 July 2007 Ó Springer Science+Business Media, LLC 2007 Abstract The present work addresses the influence of microwave irradiation on undoped and doped vanadium phosphate catalysts. These catalysts were prepared via VOPO 4  2H 2 O. The catalyst’s precursors‘ VOHPO 4  0.5H 2 O were subjected to microwave irradiation and comparison was made with the conventional heating. The interaction of these complex materials with microwave and the addition of several doponts (Nb, Bi, Co, Mo) provide interesting improvements in catalyst preparation found to be a faster, develop higher surface area, higher activity and selectivity for the oxidation of n-butane to maleic anhydride. All the catalysts were characterized by using a combination of powder XRD, H 2 -TPR, BET surface area and SEM. Keywords Vanadium phosphate  Microwave heating  n-butane oxidation  Maleic anhydride 1 Introduction The selective oxidation of n-butane continues to receive considerable research attention. In this respect vanadium phosphate catalyst has been extensively investigated and to date it represent the sole example of a commercial catalyst for the selective oxidation of an alkane [1]. The catalytic performance of vanadium phosphates depends on the method of preparation of the catalyst precursor, VOHPO 4  0.5H 2 O [2–4], and the reaction conditions utilized for the activation in n-butane/air to form the final catalyst [2, 3]. The active catalyst comprises (VO) 2 P 2 O 7 in combination with some V 5+ phosphates, typically a II - and d-VOPO 4 , and the transformation of the precursor to the final catalyst is topotactic [4]. Hence, the preparation route and the precursor’s mor- phology is of importance in determining the eventual catalyst morphology and the performance following activation. In general, for the preparation of VOHPO 4  0.5H 2 O, V 2 O 5 is used as a source of vanadium and H 3 PO 4 is used as a source of phosphorus. Hence, a reducing agent is required to synthesis the V 4+ precursor phase and a broad range of reducing agents and solvents have been employed [2–11]. Early studies tended to use water as solvent and in this case hydrochloric acid was utilized as reducing agent. This method prepares low area materials that have VO(HPO 4 ) 2 as an impurity [4]. A major innovation was the introduction of an alcohol, typically isobutanol, as both the solvent and the reducing agent [5], and this method tends to give much higher surface area materials without the presence of impurities. Despite plentiful studies worldwide, progress in this field has been hampered by low n-butane conversion and serious catalyst deactivation due to coke formation. It is well known that the preparation method of catalyst can affect the channel structure, the acid site density, and the oxidation state and location of the vanadium species. These factors are recognized to affect the catalytic performance of n-butane conversion. Thus, this leads to the investigation of new preparation method and to the further optimization of catalyst performance. Microwave heating has been shown to be a promising technique for catalyst preparation because of its heating characteristic [12, 13]. Y. H. Taufiq-Yap (&)  A. A. Rownaghi  M. Z. Hussein  R. Irmawati Putra Laboratory for Catalysis Science and Technology, Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia e-mail: yap@fsas.upm.edu.my 123 Catal Lett (2007) 119:64–71 DOI 10.1007/s10562-007-9190-x