Influence of Milling Media on the Physicochemicals and Catalytic Properties of Mechanochemical Treated Vanadium Phosphat
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Influence of Milling Media on the Physicochemicals and Catalytic Properties of Mechanochemical Treated Vanadium Phosphate Catalysts Y. H. Taufiq-Yap • C. K. Goh • G. J. Hutchings N. Dummer • J. K. Bartley
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Received: 7 July 2010 / Accepted: 19 November 2010 / Published online: 3 December 2010 Ó Springer Science+Business Media, LLC 2010
Abstract VOHPO40.5H2O synthesized via the alcohol reduction of VOPO42H2O was mechanochemical treated for 30 min in three different media, i.e. cyclohexane, ethanol and air. XRD results revealed that their structure became less crystalline compared to the unmilled material. SEM showed that the particles for the milled materials become smaller and unique features were observed in the different type of media used. The reactivity of the oxygen species linked to V5? and V4? were also affected by the milling process. The selectivity to maleic anhydride from n-butane oxidation were observed to increase in line with the increase in the oxygen species associated with V5? and the presence of isolated V5? phase. A correlation was observed between the crystallite size of the pyrophosphate phase at (020) plane with the maleic anhydride selectivity. Keywords Mechanochemical Vanadium phosphate Maleic anhydride n-butane oxidation
Y. H. Taufiq-Yap (&) C. K. Goh Centre of Excellence for Catalysis Science and Technology, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia e-mail: [email protected] Y. H. Taufiq-Yap Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia G. J. Hutchings N. Dummer J. K. Bartley Cardiff Catalysis Institute, School of Chemistry, Cardiff University, Cardiff CF10 3AT, UK
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1 Introduction Mechanochemistry is a chemical conversion of solids induced by mechanical processing usually milling or grinding [1]. Most efficient mechanochemistry of solid materials can be achieved in planetary ball mills. Recently, this technique has received attention in the preparation of vanadium phosphate (VPO) catalyst, where the VPO is an important industrial catalyst used in the partial oxidation of n-butane to maleic anhydride (MA) [2]. Among numerous compounds formed in VPO system, vanadyl pyrophosphate, (VO)2P2O7 is known to be the most efficient catalyst for partial oxidation of n-butane to maleic anhydride and this phase is usually obtained by activating the precursor, VOHPO4H2O in an n-butane/air gas mixture at about 673 K for an extended time period [3]. It has been shown that the mechanochemical treatment of VOHPO4H2O could impair the structure and morphology of the final VPO catalysts and, accordingly the catalytic properties [4]. One of the factors affected the effectiveness of ball milling is the media in which the miling takes place [5]. Horowitz et al. [6] found that wet milled the precursor of VPO catalysts in isopropanol for 24 h could create shear forces which is able to prevent the crystal platelets from tightly stacking together, thereby exposing more surface plane and consequently enhanc
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