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Synthesized ammonia exiting a reactor with hydrogen and nitrogen can be selectively absorbed by MgCl2 for renewable absorbent-based Haber-Bosch for dispersed ammonia manufacturing. Such separation can be more efficient even at elevated temperatures compared to the condensation method used in the conventional Haber-Bosch process. To determine the optimal conditions to capture and release the most ammonia per thermal cycle of the sorbent salt, the sorbent capacity was measured with varying regeneration temperature, regeneration time, and sweep rate under steady-state cycling conditions. In all cases, uptake was limited to bed breakthrough, and cyclic steady state was achieved. By using a lower temperature for MgCl2 regeneration (200 °C), the working capacities were maintained comparable to those at higher desorption temperatures (∼400 °C), even without the use of inert sweep gas. Using a sufficiently high regeneration temperature (∼200 °C) allowed for sufficiently low sweep gas so that the product ammonia can exceed 72 mol % purity in a mixture of N2 and H2. These results were achieved with a short regeneration time of 20 min or less, which is an improvement from the hour-long regeneration time previously reported. These measurements identified new operating parameters for more efficient absorber design to produce economical renewable ammonia at small scale. 

Hydrogen gas is a promising renewable energy storage medium when produced via water electrolysis, but this process is limited by the sluggish kinetics of the anodic oxygen evolution reaction (OER). Herein, we used a microkinetic model to investigate promoting the OER using programmable oxide catalysts (i.e., forced catalyst dynamics). We found that programmable catalysts could increase current density at a fixed overpotential (100-600× over static rates) or reduce the overpotential required to reach a fixed current density of 10 mA cm-2 (45-140% reduction vs static). In our kinetic parametrization, the key parameters controlling the quality of the catalytic ratchet were the O*-to-OOH* and O*-to-OH* activation barriers. Our findings indicate that programmable catalysts may be a viable strategy for accelerating the OER or enabling lower-overpotential operation, but a more accurate kinetic parametrization is required for precise predictions of performance, ratchet quality, and resulting energy efficiency. 

Renewable 1,3-butadiene (1,3-BD, C4H6) was synthesized from the tandem decyclization and dehydration of biomass-derived tetrahydrofuran (THF) on weak Brønsted acid zeolite catalysts. 1,3-BD is a highly solicited monomer for the synthesis of rubbers and elastomers. Selective conversion of THF to 1,3-BD was recently measured on phosphorus-modified siliceous zeolites (P-zeosils) at both high and low space velocities, albeit with low per-site catalytic activity. In this work, we combined kinetic analyses and QM/MM calculations to evaluate the interaction of THF with the various Brønsted acid sites (BAS) of Boric (B), Phosphoric (P), and Sulfuric (S) acid modified silicalite-1 catalysts toward a dehydra-decyclization pathway to form 1,3-BD. Detailed kinetic measurements revealed that all three catalysts exhibited high selectivity to 1,3-BD ca. 64–96% in the order of S-MFI > P-MFI > B-MFI at a given temperature (360 °C). Notably, the S-MFI maintained a selectivity >90% for all evaluated process conditions. The computational results suggested that the nature of the Brønsted acid sites and the adsorption energetics (relative THF-acid site interaction energies) are distinct in each catalyst. Additionally, the protonation of THF can be improved with the addition of a water molecule acting as a proton shuttle, particularly in S-MFI. Overall, S-containing zeosils exhibited the ability to control reaction pathways and product distribution in dehydra-decyclization chemistry optimization within microporous zeolites, providing another alternative weak-acid catalytic material. 

The growing global plastic waste challenge requires development of new plastic waste management strategies, such as pyrolysis, that will help to enable a circular plastic economy. Developing optimized, scalable pyrolysis reactors capable of maximizing the yield of desired products requires a fundamental understanding of plastic pyrolysis chemistry. Accordingly, the intrinsic reaction kinetics of polypropylene pyrolysis have been evaluated by the method of pulse-heated analysis of solid reactions (PHASR), which enables time-resolved measurement of pyrolysis kinetics at high temperature absent heat and mass transfer limitations on the millisecond scale. Polypropylene pyrolysis product evolution curves were generated at 525°C–625°C, and the overall reaction kinetics were described by a lumped first-order model with an activation energy of 242.0 ± 2.9 kJ mol−1 and a pre-exponential factor of 35.5 ± 0.6 ln(s−1). Additionally, the production of solid residues formed during polypropylene pyrolysis was investigated, revealing a secondary kinetic regime.