Study On Oxidative Dehydeogenation Of Propane Over Vanadium Magnesium System Catalyst

The?-zeolite and?-Al₂O₃ were used as carriersr,V was used as the active component,and Mg was used as the modification aid to produce the supported vanadium-magnesium catalyst.The vanadium-magnesium spinel?MgV₂O₄?was produced by co-precipitation method.A method for the detected of the V valence in vanadium-based catalysts by cyclic voltammetry was established.Using XRD,CV and quartz micro-reactor,The adsorption of propane and propylene and their changes in temperature programmed were investigated by in-situ infrared spectroscopy.The experimental result showed that:1.The CV curves of vanadium-based catalysts were measured by cyclic voltammetry with scanning voltage of-0.6⁰.9 V,sensitivity of 1 mA and scanning rate of 0.05 V/s under electrolyte pH=1.0.The result showed that:the reduction potential for V⁵⁺were-0.38V and0.32V,V⁴⁺was-0.23V and 0.23V,and V³⁺was-0.13V and 0.38V.The reduction potential of MgV₂O₄ has a good correspondence with the two potentials of V³⁺.It is feasible to detect the valence of V in the vanadium-based catalyst.2.The MgV₂O₄ catalytic behavior result showed:the selectivity of propylene was 55.6%,and the conversion of propane was 11.2%.The CV results showed that the reduction peak of-0.13V decreased after the reaction,the reduction peak at 0.38V was enhanced,The 0.38V may be the stable characteristic potential of V³⁺.3.The 8V/?catalyst had good activity in V/?series catalyst,and the activity of 8V4Mg/? catalyst was better after added Mg,the selectivity of propylene was 73.6%,and the conversion of propane was 12.4%.The CV result showed that the vanadium was presented as V³⁺both in the V/?and V-Mg/?catalyst.the V³⁺was converted into the V⁵⁺or other VO_X during the reaction.4.The 8V/?-Al₂O₃ catalyst had good activity in V/?-Al₂O₃ series catalyst,and the activity of8V4Mg/?catalyst is better after added Mg.The CV result showed that the vanadium was presented as V³⁺or V⁵⁺,which were mutually converted during the reaction.5.The adsorption of propane on?-zeolite,8V/?and 8V4Mg/?catalyst,and temperature-programmed reaction on V/?-Al₂O₃ catalyst and MgV₂O₄ were studied by in-situ infrared spectroscopy,The results showed that the addition of vanadium was beneficial to the adsorption of propane on the catalyst,the adsorbed propane tend to deep oxidation to CO₂ when V content was low,and propylene selectivity was low when V content exceeded 8%.The alkali metal Mg favored the selectivity of propylene,and V=O characteristic peak was appeared during the reaction for MgV₂O₄ catalyst.6.Using LAMMPS-ReaxFF molecular simulation showed that the first active-intermediate was O₉₀V₄₂2 cluster during the reaction.The O₂V was related to the elementary reaction on V₂O₅in the absence of oxygen.