The chemical industry relies heavily on light olefins and acetylene as primary building blocks for plastics, pharmaceuticals, and other high-value products. Currently, these unsaturated C2 hydrocarbons are produced from fossil resources, using processes that emit significant amounts of CO2 and deplete finite reserves. Shifting to a circular carbon economy requires regarding CO2 not only as a pollutant but as a carbon feedstock. By reducing CO2 with renewable hydrogen, it is possible to store energy in the chemical bonds of synthetic hydrocarbons, such as ethylene and acetylene. However, direct CO2-to-hydrocarbon processes are kinetically limited by the CO2 activation barrier and thermodynamically by the stability of hydrocarbon products.
This thesis investigates two strategies to overcome these limits and tune product distribution toward unsaturated C2 hydrocarbons: (i) a tandem-reactor approach and (ii) a tandem-catalytic approach. To achieve this, a reactor platform comprising a high-pressure fixed-bed microreactor with online analysis was developed.
First, to enable the tandem-reactor strategy, the initial CO2 methanation step was optimized. Bayesian optimization was utilized to screen and optimize Ni-Co/Al2O3 catalysts for methanation, resulting in a nearly 50% increase in methane space-time yield relative to earlier-synthesized catalysts. This optimized platform was then integrated with a novel nanosecond-pulsed dielectric-barrier discharge plasma reactor, with online gas chromatography, mass spectrometry and synchronized power measurements. This CH4-mediated tandem-reactor approach enabled the first-of-a-kind acetylene production from CO2 under near-ambient conditions, achieving 98.3% total CO2 conversion. Multi-objective Bayesian optimization minimized the energy cost per olefin molecule along a Pareto front.
Next, a tandem-catalytic approach was also pursued, where bifunctional Ga2O3-In2O3 catalysts on chabazite zeolite were synthesized to convert CO2 into hydrocarbons in a single reactor. A catalyst structure-performance relationship was established as a function of Ga/In ratio using advanced characterization techniques. The optimal composition yielded smaller crystallites with more abundant surface oxygen defects and reduced Ga species, along with moderate CO2 and C2H4 adsorption strengths and a balanced acid site distribution, achieving an ethylene selectivity of 45.9% among C2+ hydrocarbons. Then, the role of zirconia incorporation into GaInOx nanoparticles, paired with chabazite zeolite was explored using in situ DRIFTS and NAP-XPS. Zr increased the oxygen defect density while limiting indium reduction, enhancing light olefin selectivity to 73.6% at 16.8% CO2 conversion and suppressing methane from 24.4% to 8.1%. Zr-rich catalysts exhibited less coke and improved stability, attributed to water retention at the Zr-rich interface, inhibiting zeolite Brønsted acid sites.
Finally, a techno-economic analysis benchmarked these tandem s
