CATALYTIC CONVERSION OF CO2 TO METHANOL OVER SUPPORTED INTERMETALLIC CATALYST
Venue and Date:- Department of Chemical Engineering, will be held at 11:00 am on 22 June 2020, Monday.
ABSTRACT
The global warming and change in climatic conditions due to rising concentration of CO2 in atmosphere are the most important challenges of the 21st century. Catalytic conversion of CO2 to methanol will not only check global warming but will also provide an alternative source of fuel. In this thesis, a detailed experimental investigation into direct hydrogenation of CO2 to methanol has been carried out. Herein, initially, a comprehensive and comparative thermodynamic analysis of various CO2 hydrogenation processes including methanol synthesis was performed in a wide range of reaction conditions. The thermodynamic limitations of the reaction and favourable range of reaction-parameters were then found to be helpful in the experimental study. In the experimental work, a new class of intermetallic catalysts was prepared and tested for the CO2 hydrogenation to methanol. The alloys of Ga with Pd and Ni over SiO2 support were synthesized using different preparation methods to get the most desirable catalytic properties. The prepared catalysts were characterized by various techniques like XRD, TEM-EDX, SEM, BET, H2-chemisorption, H2-TPR, CO2-TPD, ICP-MS, and FTIR. The activity test of the H2-reduced catalysts was carried out in a differential plug flow fixed bed reactor. From the catalyst screening, the Ga3Ni5/SiO2 catalyst prepared through co-precipitation method (Ga3Ni5-CP) was found to be most active for methanol synthesis among all the catalysts including Pd2Ga/SiO2. Further analysis like the influence of various reaction parameters on catalytic activity to get the best set of parameter values was performed over co-precipitated Ga3Ni5/SiO2 catalyst. The co-precipitated Ga3Ni5/SiO2 catalyst was found to be more active than the traditional Cu/ZnO/Al2O3 methanol catalyst under the same reaction conditions. A detailed kinetic analysis of methanol synthesis from CO2/H2 including RWGS reaction over Ga3Ni5 catalyst was performed in a continuous differential plug flow fixed bed reactor after identifying the mass transfer resistance-free regime. From the kinetic study, the hydrogenation of formate to give surface-bound H2COO was found to be the rate-determining step. The kinetic model was found to follow a single site mechanism and was found consistent with literature reports. The Ga3Ni5-CP also showed better stability followed by Ga3Ni5-IWI and Ga3Ni5-CE respectively. From the deactivation analysis, the loss in catalytic activity is attributed to the loss of active surface area due to sintering and Carbon-deposition as evident from the spent catalyst characterizations. The higher activity was related to the highly accessible Ga3Ni5 surface during methanol synthesis. From the deactivation kinetics, the deactivation rate of Ga3Ni5 catalysts was found to fit the first order power-law model and the order of their deactivation constants followed, Ga3Ni5-CE > Ga3Ni5-IWI > Ga3Ni5-CP.