Poly(ethyleneimine)-impregnated sorbents are prepared using a hierarchical silica support with bimodal meso-/macroporosity. The sorbents behave unexpectedly during CO 2 adsorption from simulated air and flue gases (400 ppm and 10% CO 2 ) at a fixed temperature, as compared to systems built on commonly studied mesoporous materials. The results demonstrate that (i) impregnation methods influence the efficacy of sorption performance and (ii) the sorbents show almost similar uptake capacities under 400 ppm and 10% dry CO 2 at 30 °C, exhibiting step-like CO 2 adsorption isotherms. These unusual observations are rationalized via control experiments and a hypothesized sorption mechanism. While the sorption performance near room temperature is unexpectedly identical under 400 ppm and 10% CO 2 conditions, there is an optimal temperature at each gas concentration where the uptake is maximized. The maximum sorption capacities are 2.6 and 4.1 mmol CO 2 /g sorbent at the optimized sorption temperatures using 400 ppm and 10% dry CO 2 , respectively. The presence of water vapor under 400 ppm CO 2 conditions further improves the sorption capacity to 3.4 mmol/g sorbent, which is the highest capacity under direct air capture conditions among known amine sorbents impregnated with a similar polymer, to the best of our knowledge.

A single-component, recyclable heterogeneous palladium nanoparticle catalyst is described for the selective hydrogenation of alkynes. The palladium nanoparticles are generated through reduction of Pd(II) species loaded into a mesoporous silica material functionalized with branched poly(ethyleneimine) polymers. An array of composite catalysts with similar polymer composition, palladium loading, and nanoparticle size (∼2 nm) are prepared to understand the importance of the polymer attachment method, the metal reduction method, the polymer molecular weight, and the oxide porosity. Each catalyst shows excellent activity in room temperature, liquid phase hydrogenation of diphenylacetylene to selectively produce cis-stilbene. Interestingly, it was found that the rate of over-hydrogenation could be significantly reduced by increasing the support porosity and using a high-molecular-weight polymer. These single-component catalysts are competitive with the best palladium catalysts known for the selective liquid phase hydrogenation of alkynes and can be easily recovered and recycled with no leaching of palladium detected, retaining high activities and selectivities over multiple cycles with a simple regeneration procedure.

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Physical aging or degradation of amine-containing polymers and supported amine adsorbents is a critical issue that could limit the practical application of such materials for CO 2 capture. However, to date, there is a scarcity of studies that evaluate the long-term stability of aminebased sorbents without the exclusive use of accelerated aging tests. Here, we demonstrate that extended aging (∼2 years) of linear poly(propylenimine) (LPPI) confined in mesoporous silica (SBA-15) supports does not drastically impact the CO 2 adsorption performance under simulated flue gas (10% CO 2 ) and direct air capture (DAC, 400 ppm CO 2 ) conditions, although the behavior of the aged sorbents and polymers in the two CO 2 concentration regimes differs. The sorbents made with aged LPPI have modestly decreased CO 2 uptake performance (≲20% lower) compared to the fresh polymers, with overall good CO 2 cycling performance. The data indicate that only slow degradation occurs under the deployed ambient storage conditions. Even after extended aging, the LPPI-based sorbents preserved their ability to display stable temperature-swing cycling performance. In parallel, the impact of blending LPPI polymers of different number-average molecular weights, M n , is evaluated, seeking to understand its impact on adsorbent performance. The results demonstrate that the blends of two M n aged LPPI give similar CO 2 adsorption performance to adsorbents made from a single-M n LPPI, suggesting that molecular weight will not negatively impact adsorbent performance in the studied M n range. After an accelerated oxidation experiment, the aged LPPI sorbents retained a larger portion of the samples' original performance when cycling under simulated flue gas conditions than under DAC conditions. However, in each case, the oxidized sorbents could be cycled repeatedly with consistent uptake performance. Overall, these first of their kind extended aging tests suggest that LPPI-based amine adsorbents offer promise for longterm, stable use in carbon capture applications.