Carbon Supported Metal Carbide Catalysts for the Reduction of Carbon Dioxide

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Development of active and selective catalysts for the conversion of CO2 into valuable products is a promising strategy for reducing the environmental impact of CO2 released from the use of fossil fuels. The manufacture of these catalysts should also consider the use of waste materials and reduction of chemicals needed to decrease energy and resource consumption while being economically feasible. The aim of this research was to prepare a molybdenum-carbide catalyst from petroleum coke (petcoke), an abundant waste material from oil refining, with comparable activity and selectivity to other catalysts studied for the reduction of CO2 by H2. The process of converting petcoke into a catalyst involved increasing its porosity and carburizing added Mo using microwaves or electrical heating, focused on eliminating the need for methane and/or hydrogen for its preparation. Due to pyrophoricity risks, a multiple-test rig was built to study the catalysts preventing their exposure to air or passivation gases. The petcoke-based carbon prepared had higher surface areas and pore volumes (~2000 m2/g and > 1 cm3/g) than other commercial carbons (1000-700 m2/g and ~0.5 cm3/g) which enhanced the catalytic performance towards CO2 reduction. Microwave-assisted synthesis reduced the carbide preparation time from 15 h to 8 min. However, the resulting samples showed low CO2 conversion between 1.6-1.2 %. The catalysts prepared using a furnace showed a maximum CO2 conversion of 5.2 % and selectivity towards CO above 95.8 % after 24 h of reaction comparable to that previously reported for Pt based catalysts. Further investigations evaluated the improvement of the catalyst by re-using the petcoke activation chemical as a promoter. Alkali from petcoke activation with KOH moderately improved CO selectivity (97.4 % to 99.5 %) and stability (deactivation from 34 % to 26%) but decreased CO2 conversion by 2 %. Probable site blockage at high loadings of potassium (~5 wt%) indicate that further washing is needed to decrease the potassium concentration and maximize the promotion effect. The findings from this thesis provided insights on the preparation methods of Mo2C catalysts and alternative technologies for CO2 capture and re-utilization that is becoming a major cost in the energy sector.
petroleum coke, activated carbon, carbothermal reduction, molybdenum carbide, CO2 conversion, reverse water-gas shift reaction
Virla Alvarado, L. D. (2018). Carbon Supported Metal Carbide Catalysts for the Reduction of Carbon Dioxide (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from doi:10.11575/PRISM/31881