Electrolysis of carbon capture liquids is extensively studied for production of commodity chemicals such as ethylene and syngas coupled with near neutral carbon emissions. The cathode product consists of complex gas mixtures whose separation remains a major bottleneck, owing largely to the limited selectivity of electrocatalysts. This study proposes a cost-effective and energy-efficient solution for downstream separations from CO2RR electrolyzers. We investigate high–silica chabazite zeolite (CHA) hollow fiber membranes (ZHFMs) as a separation platform for gas mixtures relevant to (bi)carbonate electrolysis due to their superior molecular sieving capabilities and high surface-to-volume ratios. We evaluated membrane performance at 25–150 °C with different gas compositions and sweep gas flow rates (0–200 sccm). Single component gas permeation data were used to parameterize a Maxwell-Stefan modeling framework, enabling semi–quantitative prediction of multicomponent permeation behavior. The calibrated model was employed to examine the influence of operating variables such as temperature, pressure, and feed composition on separation performance and gas recovery. To demonstrate reproducibility, 10 successive batches of ZHFMs were synthesized, and the single component H2/C2H4 selectivity was found to be 49 ± 5 on a random sample from each batch. We tested scalability, onset of temperature fatigue, and long-term stability to evaluate membrane robustness, with consistently good performance demonstrated across multiple cycles. A multi-fiber module was developed and operated without use of sweep gas, emulating typical industrial conditions. The module maintained excellent H2 permeance (∼1000 GPU) and H2/C2H4 separation factor ∼ 30 over 100 h in a simulated multi-component feed representative of the gas phase cathode product.

Mechanochemical processing is an attractive and scalable approach for the upcycling of polymers. The complex and dynamic environment in ball milling, however, makes gaining insight into the physicochemical nature of the collisions driving mechanochemistry challenging, which, in turn, hampers the optimization of these processes. We used controlled single impacts followed by multiple spatially resolved analytical methods (focused ion beam microscopy, Raman spectro-microscopy, and small-angle X-ray scattering) and material point method simulations to gain unprecedented information about mechanochemical depolymerization of poly(ethylene terephthalate). These measurements highlight the contributions of plastic deformation, amorphization, and depolymerization during the transfer of kinetic energy in collisions relevant to ball mills and will enable reactor models based on fundamental kinetics.

Plastic waste accumulation necessitates innovative recycling approaches to achieve sustainability goals. Mechanochemical depolymerization offers a solvent-free, energy-efficient route to convert polymers into valuable monomers. In addition to their chemical properties, the way that polymers absorb kinetic energy is a key parameter of any mechanochemical process. This perspective explores the principles underpinning mechanochemical recycling, emphasizing how deformation and localized transient heating mediate energy transfer between impacts and localized excitations. Key factors such as polymer crystallinity, molecular weight, viscoelasticity, and thermal effects are analyzed to elucidate their role in energy transfer mechanisms during ball milling. This work establishes a foundational framework for the design and optimization of mechanochemical recycling by connecting polymer response to mechanical energy with the intention to improve depolymerization efficiency. Future research opportunities are outlined to advance the integration of polymer science and mechanochemistry for scalable, sustainable plastic upcycling.

This study explores a thermally assisted mechanochemical approach alternative to conventional cement synthesis as a potential to produce hydraulically reactive calcium silicate phases. Ball milling of mixed CaO/SiO2 feedstocks at temperature ranges 100-300 degrees C increases the formation of the Ca-O-Si bonds and precursor reactivity. Spectroscopic analyses (FTIR, MAS-NMR, XPS) indicate increasing amorphization with milling temperature, attributed to improved mixing and thermally assisted diffusion. Upon hydration, all treated samples exhibit exothermic heat release, with the sample prepared at 300 degrees C showing the most pronounced reactivity. Thermal analysis reveals weight loss consistent with C-S-H formation, confirming cement-like behavior. Importantly, this process favors the formation of reactive phases at particle surfaces, which may enable significant hydraulic reactivity even when bulk decarbonization is avoided. In summary, moderate thermal input during milling promotes structural activation and enhances downstream hydraulic reactivity, providing a proof-of-concept for energy-reduced cement precursor processing.

Captured carbon dioxide (CO2) streams contain impurities that must be removed to meet specifications for safe transport, storage, and utilization. Among these impurities, oxygen poses challenges due to its high reactivity and potential to cause corrosion, motivating stringent purity limits below 10 ppmv. Building on recent experimental demonstrations of catalytic oxygen removal using hydrogen (H2), carbon monoxide (CO), methanol (CH3OH), and methane (CH4) as reducing agents, this study presents a technoeconomic (TEA) and life cycle assessment (LCA) of these four catalytic purification pathways. Process flowsheets were developed and simulated in Aspen Plus for CO2 streams representative of both low-temperature and high-temperature capture processes, with integrated heat recovery and energy optimization. Results showed that total purification costs were dominated by feedstock procurement and electricity consumption. Among the studied reducing agents, the CH4-assisted route achieved the lowest purification cost and highest CO2 recovery. Sensitivity analyses showed that the H2 route became competitive at H2 prices below $0.56/kg to $0.84/kg, depending on the CO2 feed temperature conditions. Environmental impacts were primarily driven by indirect CO2 emissions from raw material production and utility consumption.

Solid amine sorbents are one of the primary components of DAC technologies that allow for the removal of ultradilute CO2 from the atmosphere. A main drawback in the implementation of solid amine sorbents in industrial-scale DAC applications is their instability under certain operational or storage conditions over an extended period. In this work, the effect of storage temperature and gas composition in the storage headspace on the long-term stability of a poly-(ethylenimine)-alumina (PEI/γ-Al2O3) sorbent is explored. PEI/γ-Al2O3 sorbents with 70 and 100% pore filling are aged under varying gases (N2, O2, Ar, 0.04% CO2-N2, CO2, and ambient air) in an oven (40 °C), at common ambient indoor temperature conditions (23 °C), or in a freezer (-4 °C). The CO2 sorption capacity, as measured by thermogravimetric analysis (TGA), along with FTIR spectra of the fresh and aged sorbents, reveal that at 23 and -4 °C, storage under ambient air or inert gas (Ar) provides reasonable long-term stability, with <13% degradation over 12 and 5 months of storage. Interestingly, with storage at 40 °C, similar levels of deactivation were observed under pure O2 and N2 after 4 months of storage, which suggests that nonoxidative thermal reactions can occur under prolonged storage conditions under N2. In contrast, with storage under CO2, sorbent degradation is substantially suppressed compared to storage under N2, ambient air, O2, or Ar, yielding sorbents with no observable loss in capacity after 2 months, compared to a 66, 63, and 62% loss under N2, ambient air, and N2 in the same period at 40 °C, respectively. Overall, these findings provide guidance for practical amine sorbent storage in academic or industrial settings where amine sorbents are used for carbon capture.

Ball mill grinding has significant potential to process solid feedstocks by inducing mechanochemical reactions. Since the intrinsic kinetics of high-velocity milling systems can be difficult to observe experimentally, the driving forces of mechanochemical reactions can be challenging to identify. Mechanochemical reaction is driven by several mechanisms, each with distinct timescales of chemical excitation: the mechanical activation of the feed that creates meta-stable or unstable structural configurations, the heightened temperatures in local hot-spots, and the elastic chemical bond deformations during impact. To derive rigorous kinetic expressions for mechanochemical ball milling, it is essential to determine the extent to which these forms of excitation persist between impacts with grinding media. This study quantifies the timescale of high-energy collision occurrence and re-occurrence on powder volume elements. As a model system, we investigate the kinematics of polymeric powder beds in a vibratory ball mill. Granular trajectories are computed with discrete element method (DEM) simulations to define particle-level collision rates and energetics, distinct from lumped performance metrics. We show that in the absence of particle comminution and accumulated plastic deformation, the mechanical energy transferred from grinding media to powder does not typically persist between tail-end collisions, for a range of operating conditions and powder properties. This indicates that fast-decaying local environments of heightened chemical reactivity are underutilized. We additionally visualize the spatial distribution of energetic collisions on feedstock particles within the vessel, and extend the findings of this study to more general classes of particulate feeds by considering varied reaction energy thresholds and powder bed contact parameters.

The success of direct air capture (DAC) of CO2 depends on sorbents that combine high capacity, low energy requirements, and long-term durability. Amine-based sorbents—including solid-supported aminopolymers, grafted amines, and amine-functionalized resins—remain the leading candidates, but their limited lifetimes drive up costs and constrain deployment. In this review, we outline the current understanding of amine-based sorbent degradation with an emphasis on clearly identifying what is known about structure-property-performance relationships, as well as important knowledge gaps. More specifically, we discuss how polymer chemistry, sorbent design variables, and environmental and process conditions contribute to performance loss. In parallel, we outline how advances in spectroscopy, modeling, and accelerated testing are beginning to illuminate chemical and physical degradation mechanisms. Looking forward, we identify future research directions that will be critical for gaining a deeper understanding of degradation, as well as opportunities for developing innovative mitigation strategies for improving the lifetime of amine-based sorbents.

The mechanochemical depolymerization of commercial PET feedstocks is successfully demonstrated for a variety of samples representing consumer products without the need for specific sample pretreatment. Complete depolymerization is achieved within 20 min by ball milling it with NaOH under ambient conditions. Samples with a higher initial content of amorphous domains depolymerize more rapidly, as collision energy is more effectively utilized for creating reactive interfaces between NaOH and PET. While thickness has a minor effect compared to crystallinity, thicker samples experience lower reaction rates because their accessible surface area is limited. For low-packing density samples, a reduced rate of depolymerization could be expected due to restricted ball motion, but this effect is overcompensated by the ease at which these samples form interfaces. The success of mechanochemical alkali-depolymerization of PET in a ball mill presents an opportunity for industrial implementation, offering a sustainable approach to polymer upcycling due to its mild reaction conditions and minimal solvent requirements.

This study demonstrates that partial oxidative regeneration of spent ferrierite zeolite (H-FER / H-ZSM-35) used in skeletal 1-butene isomerization effectively restores catalyst activity, while residual carbonaceous deposits significantly reduce the catalyst startup time. By employing catalyst characterization techniques such as X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), operando UV-Vis spectroscopy, and density functional theory (DFT) calculations, the findings reveal that oxidative regeneration of spent H-FER at 500 degrees C removes external polycyclic aromatic carbonaceous deposits that block pore mouths. However, this process also promotes the migration of internal carbonaceous deposits to the external surfaces, where they condense into polycyclic aromatic structures. These structures obstruct pore access until the total carbonaceous deposits are reduced to below similar to 1 wt%. Beyond this threshold, further oxidative removal of coke is not beneficial, as the residual carbonaceous deposits promote catalyst startup in subsequent cycles and inhibit strong acid sites that contribute to side product formation. In addition to offering a practical strategy for accelerating catalyst startup, this partial regeneration approach provides valuable insights into the nature of catalytically active species at the pore mouth. The results suggest that residual carbonaceous fragments can enhance catalyst activation speed by up to threefold. Utilizing these residual deposits as both coke precursors and selective poisons represents a promising method for efficient partial oxidative regeneration of catalysts affected by coke deposition.

Abstract Formic acid oxidation (FAO) over platinum electrocatalysts has been widely studied as an anodic reaction for fuel cell technologies, but the lack of experimental data accounting for the binding strength of formate intermediates under relevant electrochemical conditions hampers optimization of catalyst–electrolyte interfaces. In this work, we use two-dimensional correlation surface enhanced infrared adsorption spectroscopy (2D COS SEIRAS) to probe the adsorption of formic acid between 25 and 65 °C, and to determine the adsorption enthalpy of formate on platinum (−46 ± 3 kJ mol–1 at −0.2 V vs RHE). Adsorption isotherms collected at different potentials reveal that positively charged platinum surfaces facilitate higher formate coverages despite weaker binding strength. Comparison of adsorption enthalpies and electro oxidation selectivities over platinum and copper catalysts suggests that binding strength to a metal surface is an important descriptor of FAO catalysis. This works provides a method to reliably determine adsorption enthalpies of reaction intermediates under different electrochemical conditions, which will be key to better engineer catalyst systems that promote oxidative conversion of organics.

Large-scale CO2 electrolyzers will likely operate at elevated temperatures, but the effect of temperature on the microenvironment near copper catalysts is largely unknown. In this work, we use confocal Raman spectroscopy to reveal that the local pH is a critical parameter controlling product formation during CO2 reduction at elevated temperatures. We found that higher temperatures lead to stronger pH gradients consisting of greater surface to bulk pH differences over shorter boundary layers. At -0.6 V, the surface to bulk pH difference at 75 °C was 1.8 units higher than that at 25 °C just from the effect of temperature alone. These results imply that most CO2 electrolyzers operating at elevated temperatures were evaluated under much more alkaline microenvironment conditions than previously conjectured at 25 °C. Correlation between surface pH and product analysis shows that a high surface pH (9.9) is beneficial for multicarbon products formation below 45 °C. However, above 55 °C when the surface pH (10.3) becomes too high due to increased surface-bound hydrogen coverage, hydrogenation of C1 intermediates is favored, thus compromising carbon-carbon coupling toward C2+ products.

When catalyzing a reaction comprising elementary reaction steps that demand both strong and weak adsorption of sequential intermediates to complete a full cycle, catalytic metals often exhibit reactivity compromises, known as Sabatier constraints. Herein, computational and experimental findings suggest that dynamic modulation of the catalyst spin state can provide a new handle to overcome such limitations via low- and high-spin catalysis for ammonia decomposition, which is a reaction that exemplifies Sabatier constraints due to the difficulty in achieving strong NH3 binding as well as weak *H and *N binding for efficient H2 and N2 formations, respectively. We demonstrate that the self-heating ferrimagnetic Ru/Fe3O4 catalyst operating under an alternating magnetic field (AMF) exhibits at least a 5-fold enhancement in activity relative to standard thermal operation below 400 °C. The key benefit comes from the time-varying magnetic flux within the catalyst under AMF, enabling rapid electronic responses at the Ru sites that mitigate Ru nitridation by transiently inducing a high-spin configuration of the metal. These findings highlight AMF-driven catalysis as a general reaction strategy for dynamically regulating catalyst electronic states and, in turn, surface intermediates, thereby overcoming the often-encountered Sabatier constraints in various catalytic reactions.

Mechanochemical depolymerization in a ball mill can be used to convert poly(styrene) (PS) into monomeric styrene under milder conditions than thermal depolymerization. Continuous sampling of product flows shows that the rate of styrene formation increases significantly when PS powder is converted into a cohesive state, a viscous, continuous material phase that tends to coat the grinding spheres, once the temperature of the grinding surfaces approaches the PS glass transition temperature (~100°C). This enhancement is attributed to intensified mechanical shear stresses that generate favorable reaction environments for depropagation of chain-end radicals in the bulk of the cohesive state. The faster depropagation steps also increase the selectivity of styrene relative to byproducts, such as methane, benzene, toluene, and ethylbenzene.

Piezoelectric catalysts were synthesized mechanochemically by converting BaCO3 and TiO2 to BaTiO3, Na2CO3 and Nb2O5 to NaNbO3 and Bi2O3 and Fe2O3 to BiFeO3. The catalytic reactivity of BaTiO3, NaNbO3 and BiFeO3 was tested using a mechanocatalytic arylation reaction involving 4-nitrobenzenediazonium tetrafluoroborate. The observed activity in the arylation reaction showed a dependence on the abundance of piezoelectrically active anisotropic phases as measured by the pre-edge intensity in XANES spectra of BaTiO3 and NaNbO3 and distribution of crystalline phases as measured by XRD for BiFeO3. A kinetic analysis showed that the reaction over BaTiO3 was limited by the amount of diazonium salt remaining in the reaction vessel, while the reaction over NaNbO3 and BiFeO3 was limited by the generation of electron hole pairs within the piezoelectric structure. This work shows that mechanochemically produced piezocatalysts have superior structural characteristics such as greater relative abundance of anisotropic phases, higher surface areas and smaller particle sizes that led the mechanochemically produced catalysts to outperform piezoelectric commercial counterparts when tested under the same arylation milling conditions.

When supported Pd catalysts are exposed to hydrogen, the heat released from the spontaneous and exothermic Pd-hydride formation creates a reaction environment that allows for melting and hydrogenolysis of benzyl phenyl ether (BPE) under nominally ambient conditions. The intrinsic exothermicity of this hydride formation acts as an initiating force for α-O-4 ether cleavage of the BPE dimer, without the need for external heat to be applied to the reaction system. Thermogravimetric analysis with differential scanning calorimetry shows heat flows of 58, 40, and 32 W g-1 for Pd supported on carbon, silica and alumina, respectively. BPE conversion increased with increasing heat flow, which correlated with a higher Pd particle dispersion and lower heat capacity of the support. X-ray absorption spectroscopy at the Pd-K edge confirms Pd-hydride formation. This work shows that the heat released by Pd-H formation can be used as an initiator for α-O-4 ether cleavage in a solid lignin model compound.

Efficient separation and purification of polymeric mixtures is an important challenge in plastic recycling. Here we demonstrate a robust graphene oxide (GO) membrane platform capable of separating low- and high-molecular-weight poly-(styrene) (PS) in nonpolar solvents. By tuning GO membrane properties through pillaring with a polyconjugated aromatic compound (PAC) and controlled reduction, we obtain the efficient nanofiltration of poly-(styrene) in a hydrocarbon solvent, enabling the removal of monomers and low-molecular-weight oligomers. Over 600 h of continuous operation, the pillared membrane maintains a stable high flux of 8 ± 1 L m-2 h-1 and total rejection of high-MW polymer. Postfractionation, the enriched high-MW retentate has a 2-fold higher yield of styrene monomers in mechanocatalytic ball-milling depolymerization compared to unfractionated PS. Removing oligomeric diluents improves energy transfer, suppresses chain transfer, and promotes chain scission followed by chain-end depropagation. Thus, fractionation by organic solvent nanofiltration with GO membranes can enable scalable and efficient routes to mechanochemical polymer recycling.

This work examines how acid site concentration (FT-IR) and strength (NH3-TPD) as well as pore mouth accessibility modulate the activity of the microporous zeolite ferrierite (H-FER) during the skeletal isomerization of 1-butene to iso-butene. Restricting the accessibility of catalyst pores and strong acid sites is achieved by selective oxidation of residual organic structure directing agent (OSDA) through precise control of calcination conditions. Because this reaction is mediated by catalytically active carbonaceous deposits, residual OSDA affects their formation. This work demonstrates that small amounts of residual OSDA (similar to 0.2 wt%) are beneficial to the reaction under industrially relevant reaction conditions in three ways. Selective poisoning of strong BAS with OSDA nearly halves the amount of dimerization and cracking byproducts and improves catalyst lifetime. Simultaneously, carbonaceous fragments of the OSDA act as coke precursors and help shorten the startup time. Hence, catalyst lifetime may be significantly improved through both optimal pretreatment conditions and by designing catalysts with an increased number of accessible pore mouths.

This work studies the effect of oxygen vacancies in a silica-doped ceria support on the mechanism of HDO reaction of phenol, m-cresol, xylenol and anisole over Pd-based catalysts. Increasing the silica content increased the density of oxygen vacancies due to the decrease in the CeO2 crystallite size. The addition of silica also promoted the reaction rate for HDO of phenolic compounds, whereas the rate for HDO of anisole remained approximately constant. These results revealed that the oxygen vacancies promoted the cleavage of the C-OH bond of phenolic molecules. Moreover, the presence of an electron donor on the aromatic ring reduces the energy barrier necessary for the cleavage of the Carom-OH bond. In the case of anisole, this molecule adsorbs on the Ce cations close to the metallic particles and then, the variation of the concentration of oxygen vacancies does not affect the rate of HDO.