Investigation on Integrated CO2 Capture and Conversion Performance of Ni-CaO Dual-Function Materials Pellets: Effect of Ni Loading and Optimization of Operating Parameters

Integrated CO2 capture and utilization (ICCU) has been regarded as an innovative strategy to realize large-scale CO2 emission reduction. The rational design of robust dual-function materials (DFMs) and the optimization of operating parameters are essential for the intensification of the ICCU process. In this work, Ni-CaO DFMs pellets with Ni loadings varying in the 1–20 wt % range are prepared for CO production via integrated CO2 capture and reversed water gas shift (RWGS) reaction. The effect of Ni loading on the structure–reactivity relationships of the Ni-CaO DFMs pellets is investigated. CO2 capture capacity decreases noticeably at higher loadings of 15 and 20 wt % due to reduced surface basicity. Increased Ni loading enhances reducibility but results in increased Ni particle size, decreased Ni specific surface area, and inferior Ni dispersion, and CO yield thus increases first and then declines. CO2 conversion and CO selectivity are almost free from the Ni loading effect. The influences of operating parameters on the ICCU performance of the 5Ni-CaO-P DFMs pellets are investigated using an orthogonal experimental design. The influencing degree of the operating parameters on CO2 capture capacity follows the order of H2 concentration for catalyst reduction > reaction temperature > CO2 concentration > weight hourly space velocity (WHSV). Reaction temperature and H2 concentration in the RWGS stage represent the two primary factors affecting the CO2 conversion performance. Multiple linear regression analyses are performed, and regression equations for describing the relationships between the various attributes and predictors are acquired. The optimal combination of the operating variables is identified as the reaction temperature of 650 °C, WHSV of 135 000 mL/(h·gcat), 25% H2 for catalyst reduction, 10% CO2 for capture, and 5% H2 for in situ RWGS. The desired 5Ni-CaO-P sample exhibits a high CO2 uptake of 16.05 mmol of CO2/g, a great CO yield of 5.77 mmol of CO/g, a remarkable CO2 conversion of ∼99%, a great CO selectivity of ∼90%, and good stability in multiple cycles under optimized working conditions. These results will guide the rational design of DFMs pellets and lay the groundwork for their scale-up applications in ICCU.