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In order to investigate the influence of support structure properties on CO capture performances of solid amine adsorbents, a novel three-dimensional disordered porous silica (3dd) with hierarchical pore networks was developed and then compared to other three materials as adsorbent support, namely, hierarchical porous silica (HPS), MCM-41, and SBA-15. They were all functionalized with tetraethylenepentaamine (TEPA) to prepare CO adsorbents. The adsorbents' ability to capture CO was examined on a fixed-bed reactor. When these supports had 60 wt% TEPA loading, the amounts of CO captured followed the order 3dd > HPS > SBA-15 > MCM-41 at 75 °C; the adsorption capacities were 5.09, 4.9, 4.58, and 2.49 mmol/g, respectively. The results indicate that a larger pore volume can promote the dispersion of amine species to expose more active sites for CO capture. The larger pore size can decrease the CO diffusion resistance. High surface area is not an important factor in determining capture performance. In addition, compared with conventional single-size mesopores, the hierarchical pore networks can disperse the TEPA species in different levels of the channel to limit undesired loss/aggregation of impregnated TEPA species. Thus, the 3dd support exhibits the best stability and highest regeneration conversion compared to the other three supports. This work demonstrates that the rational design of adsorbent support systems can effectively relieve the trade-off between amine loading and diffusion resistance. One method to surmount this trade-off is to utilize an adsorbent platform with hierarchical pore networks. Thus, this work may provide a feasible strategy for the design of CO solid amine adsorbents with high capture amount and amine utilization efficiency.

A trimodal porous support with special trimodal pore structure has been prepared by physically mixing the silica gel (HPS) and SBA-15 and then devoted to fabricate TEPA-functionalized adsorbent for CO 2 capture. The trimodal multistage mesopores structure can promote the TEPA dispersion and mitigate the mass-transfer resistance in the adsorbent and, hence, improve capture performance, compared to the single mesoporous support. The influence of the mass ratios of HPS to SBA-15, amine loaded amount, CO 2 concentration, adsorption temperatures, and water vapor were studied. The CO 2 -saturated adsorption amount of 5.05 mmol/g was obtained at 75 °C in dry N 2 flow containing 15 vol % CO 2 when the mass ratio of SBA-15 to HPS was 1:2 with 50 wt % TEPA loadings. Moreover, the CO 2 -saturated adsorption amount presented a 16% improvement in humid N 2 flow containing 15 vol % CO 2 flow at 75 °C. In addition, the S2HPS-TEPA50% also demonstrated good stability after 10 adsorption/desorption cycles. Based on in situ DRIFTS results of CO 2 adsorption/desorption process, the reaction mechanism of CO 2 with active sites was proposed by analyzing the relationships among variations of intensities of functional groups during the reaction. The intraparticle diffusion model was adapted to study CO 2 kinetics and the intraparticle diffusion prediction indicated that boundary layer diffusion was the rate-controlling step in the process of CO 2 capture. Overall, these results indicate that S2HPS-TEPA50% is promising for CO 2 capture.