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Kinetics of propylene oxidation to acrolein over bismuth molybdates

The transformation of alkanes/alkenes to useful intermediates is of significant importance in the chemical industry. In this study the physico-chemical properties and the catalytic active forms of the bismuth molibdates (Bi-Mo) were investigated using selective oxidation of propylene into acrolein (H2C=CHCHO) as a model reaction. Different methods for preparation of Bi-Mo oxides were used, with focus on spray drying of precursor solution as an advanced method of catalyst preparation. The influence of preparation conditions, such as temperature, feed flow rate and flow rate of the atomization air on morfology, physico-chemical and catalytic properties of the prepared catalysts was investigated. Prepared catalysts were studied using several techniques, such as XRD, SEM, FTIR, Raman spectroscopy, laser diffraction and surface measurements (nitrogen adsorption/desorption). Catalytic properties of the bismuth molibdates during were studied in conventional fixed-bed reactor operating under atmospheric pressure and at different reaction conditions. The reaction was performed in the temperature interval from 623 to 723 K and at various space times. High purity synthetic air was used as an oxidant. Reaction was performed at different feed gas molar ratio of propylene, air (oxygen) and nitrogen. The catalysts activity for propylene oxidation was evaluated from the overall conversion of propylene when the reaction reached steady-state. Selectivity was calculated as the amount of the desired product (acrolein) obtained per amount of consumed reactant (propylene). The one-dimensional (1D) heterogeneous model of the tubular reactor was applied based on the following assumptions: steady state and isothermal conditions, plug flow and negligible pressure drop through the catalyst bed, constant volume of the reactants, negligible intraphase mass transfer resistance and chemical reaction on the catalyst surface. The obtained experimental kinetic data were correlated with two kinetic models: simple power law rate equation and more complex mechanistic kinetic model. Numerical methods for solving model equations and parameter estimation procedure were described and obtained results were discussed. The objective of study was to correlate morphology, physico-chemical and catalytic properties of bismuth molybdate catalysts with the preparation conditions in order to obtain additional information needed to prepare an efficient catalyst.

bismuth molybdates; catalytic properties; reaction kinetics; spray drying

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