III International Conference

PP-II-44IN-SITU XRD STUDY OF VMoNbO CATALYSTS FORMATION. INFLUENCE OFTHERMAL TREATMENT CONDITIONSKardash T.U., Bondareva V.M., Dovlitova L.S., Plyasova L.M., Andrushkevich T.V.Boreskov Institute of Catalysis SB RAS, Novosibirsk, RussiaE-mail: kardashtat@mail.ruIn-situ and ex-situ XRD study of active phase formation in VMoNbO catalysts during thethermal treatment in air, in medium with low oxygen content and in helium have beenperformed. According to the data obtained genesis in oxidative conditions goes through thesame irreversible steps. On the first step layer-type compounds, disordered in slabs, appear.Subsequent thermal treatment leads to crystallization of phases. Conditions of thermaltreatment influence on the temperature range of active phase existence and on the structure ofdecomposition products. Calcination in helium leads to significantly different phasecomposition due to partial reduction of Mo and V by ammonia ions.Oxide V-Mo-Nb catalysts hold the great promise for low-temperature oxidativetransformations of ethane into ethylene, acetonitrile and acetic acid [1-3].It was found that mixed VMoNb oxide with composition V 0.23±0.0.3 Mo 1 Nb x , where х=0.20÷0.37exhibiting Mo 5 O 14 -like structure is the active phase (see Fig. 1). This structure occurs when 5+ - and6+ cations are in the certain ratio: Mo +6 /Me +5 =0.6/0.4, where Me = Mo, Nb, V.Present work is devoted to in-situ and ex-situ XRD study of active phase genesis in air, inmedium with low oxygen content (0.3 vol. % O 2 in He) and in inert atmosphere.In-situ and ex-situ X-ray powder diffraction was performed using CuKα radiation withBruker D8 diffractometer equipped with high-temperature chamber (HTK-16, Anton Paar,Austria).65Fig. 1. Dependence of the relative amount ofVMoNb compound (А), the rate of the total ethanetransformation (ethane conversion is10%), vs the Nbcontent (x) in the samples V 0.3 Mo 1 Nb x5 10 15 20 25 30 352θ, deg4321Fig. 2. XRD pattern of Mo 5 O 14 -like phase (1) and V 0.3 MoNb 0.37sample recorded in-situ in a high-temperature chamber in air at180 0 C (2), 300 0 C (3), 500 0 C (4), 550 0 C (5) 600 0 C (6) Encircledline refers to MoO 3244