A Benzothizole Linked Porous Organic Polymer for the Hydrosilylative Reduction of CO2 to Formate and Methanol
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Date
2022-03
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Abstract
The continued accumulation of anthropogenic CO2 in the atmosphere is one of the most challenging environmental problems facing society.1 Approximately 80% of the increasing CO2 that is emitted comes from the excess burning of fossil fuels. 1, 2 As world economies and populations continue to grow, predictions suggest that the amount of CO2 that is emitted will continue to rise. 1 As a result, there is ongoing research geared towards finding new alternative fuel sources that can potentially replace the burning of fossil fuels.3 One solution is to completely replace fossil fuels with green sources of energy, but a lot of this technology is underdeveloped. As a consequence, there is great interest in capturing and converting CO2 into a valuable carbon feedstock.4 5 Transforming CO2 into value- added chemicals or chemical fuels provides efficient and economical routes to help reduce CO2 emissions. However, the activation of CO2 presents a challenge due to the energy that is required to break the C=O bond (~750 kJ mol-1). Thus, the chemical activation of CO2 has been achieved by utilizing various transition metals and organo-based homogenous catalysts. 6, 7
The catalytic reduction of CO2 using hydrogen (H2) as a reductant and homogenous transition metal catalysts has proven to be effective. 7 However, this transformation is thermodynamically unfavorable, and relatively high pressures of H2 are required. On the other hand, the hydrosilylative reduction of CO2 to formates, formic acid, and methanol are thermodynamically favorable approaches. In particular, the hydrosilylative reduction of CO2 to formic acid is attractive because it is a liquid at room temperature and it contains a high volumetric hydrogen density of 53 g L-1.8 These features make formic acid a viable alternative fuel source for hydrogen-powered vehicles. In addition, the chemical reduction of CO2 to methanol is attractive because it serves as an important building block for the construction of many everyday products (i.e., plastics, paints, construction materials, etc.), and as an alternative fuel source. Although the hydrosilation of CO2 with transition metal complexes has been successful under homogeneous conditions, the utilization of heterogenous catalysts for this transformation has been underexplored. Heterogeneous catalysts are attractive for industrial applications due to their chemical stability and recyclability.
Porous organic polymers (POPs) are an amorphous class of porous polymers that have emerged as a promising platform for heterogeneous catalytic applications due to their high surface areas and superior chemical stabilities.9 In this work, a benzothiazole-linked POP (BBT-POP) has been synthesized using a solvothermal method. The BBT-POP was post-metallated with Cobalt (Co) to afford Co-BBT-POP. The Co-BBT-POP is capable of CO2 capture providing uptake capacities of 160 mg/g and 128 mg/g at 273 and 298 K respectively. Isoteric heat of adsorption (Qst) data revealed a high value of 56 kJ/mol. Additionally, the Co-BBT-POP can catalyze the transformation of CO2 to formate (89% yield) and methanol (83% yield) with very high turnover frequencies of 171 h-1 and 5360 h-1, respectively, under heterogeneous conditions. Interestingly, the Co-BBT-POP can be recycled and reused up to five times without any significant reduction in catalytic activity.
Description
Poster Division: Math, Physical Sciences, and Engineering: 3rd Place (The Ohio State University Edward F. Hayes Graduate Research Forum)
Keywords
Carbon dioxide capture, Porous Organic Polymers, catalysis