Journal of Natural Gas Chemistry 17(2008)309–312 Direct oxidation of methane to oxygenates over heteropolyanions Ouarda Benlounes 1 , Sadia Mansouri 1 , Ch´ erifa Rabia 2 , Smain Hocine 1∗ 1. Laboratoire de Chimie Appliqu´ ee et de G´ enie Chimique, Universit´ e Mouloud Mammeri, Tizi-Ouzou, Algeria; 2. Laboratoire de Chimie du Gaz Naturel, Institut de Chimie USTHB, B.P 32 El-Alia Bab-Ezzouar 16111, Alger, Algeria [ Manuscript received June 12, 2008; revised July 11, 2008 ] Abstract: Partial oxidation of methane to formaldehyde and methanol was studied at atmospheric pressure in the temperature range of 700-750 ◦ C using heteropolycompound catalysts (NH 4 ) 6 HSiMo 11 FeO 40 , (NH 4 ) 4 PMo 11 FeO 39 , and H 4 PMo 11 VO 40 , which were prepared and characterized by various analysis techniques such as infrared, visible UV, XRD and DTA. O 2 or N 2 O was used as the oxidizing agent, and the principal products of the reaction were CH 3 OH, CH 2 O, CO, CO 2 , and water. The conversion and the selectivity of products depend strongly on the reaction temperature, the nature of oxidizing agent, and the composition of catalyst. Key words: methane; oxidation; heteropolycompounds; methanol; oxygenates 1. Introduction Direct selective oxidation of methane to methanol is a process of scientific interest and industrial importance [1]. The existing process to manufacture methanol involves the steam reforming of methane to synthesis gas, followed by the high-pressure catalytic conversion of synthesis gas to methanol. The process suffers from high cost and thermal inefficiencies in the steam-reforming step [2]. Direct conver- sion of methane to oxygenate seems to be the best way to solve the problem of transporting methane to the place of applica- tion. Many studies of direct selective oxidation on the present catalysts have been carried out to get a higher selectivity of C1-oxygenates in the products [3,4]. However, the yield of C1-oxygenates for the direct selective oxidation of methane is still low and CO and CO 2 are the major products. Until very recently, attempts to find active and selective catalysts for partial oxidation of methane met with little suc- cess. Nickel catalyst, so effective for methane oxidation, was reported to yield only carbon dioxide and water with methane [5] although Xiaoxing Wang et al. [6] have reported the for- mation of significant amounts of C1-oxygenates under certain condition. Typically, B. Michalkiewicz [7] reported that the highest selectivity of methane to methanol oxidation (approx- imately 74%) at 390 ◦ C with 0.06% conversion was attained when a catalyst with the lowest iron content was used. Hyun- Sik Hahm et al. [8] found Bi-Cs-Mg-Cu-Mo to be the most suitable for methanol synthesis, with which the methane con- version and methanol selectivity were approximately 4% and 22%, respectively. Both methane conversion and methanol se- lectivityincreased with temperature. Y. Wang et al. [9] have found that iron phosphate (FePO 4 ) catalyst shows high selec- tivity to oxygenates, including CH 3 OH and HCHO, during the partial oxidation of CH 4 with H 2 -O 2 gas mixtures or N 2 O un- der relatively mild reaction temperatures (<500 ◦ C). Recent works [10] have, in fact, demonstrated that high yields to C1- oxygenates can be obtained from methane/oxygen mixtures, by carrying out the reaction at high temperature and short con- tact times, in the presence of 0.5 wt% of Fe supported on silica catalysts. This study was conducted to develop a suitable cata- lyst for the partial oxidation of CH 4 to C1-oxygenates using heteropolycompound catalysts. The effects of temperature, composition of heteropolycompounds, and oxidizing agent on methane conversion and methanol or formaldehyde selectivity were also examined. 2. Experimental 2.1. Preparation of catalysts Pure H 4 PMo 11 VO 40 (PMo 11 V) heteropolyacids were pre- pared in a classical way [11]. The ammonium-iron salts (NH 4 ) 4 PMo 11 FeO 39 and (NH 4 ) 6 HSiMo 11 FeO 40 (abbreviated as PMo 11 Fe and SiMo 11 Fe, respectively) were prepared ac- cording to literature [12]. The latter was prepared by adding aqueous solution of (NH 4 )NO 3 to a solution containing (NH 4 ) 6 Mo 7 O 24 ·4H 2 O, Fe(NO 3 )·9H 2 O, H 3 PO 4 , or Si(OH) 4 and HNO 3 (atomic ratio P or Si/Fe/Mo 1/1/11), with a pH equal to 3.5-4.0. ∗ Corresponding author. E-mail: shocine univ to@yahoo.fr