The methanol-to-olefins (MTO) process produces high value-added light olefins from non-petroleum sources. Acidic zeotypes containing cages bounded by 8-ring (small pore) windows can effectively catalyze the MTO reaction, since their cages can accommodate the necessary aromatic intermediates that produce the light olefin products that escape. While progress on the mechanisms of the MTO reaction continues, zeotype structure-reaction property relationships have yet to be elucidated. Here, we report MTO reaction results from various small pore, cage-containing SAPO/MAPOs and zeolites under the same reaction conditions. The MTO behaviors of microporous materials having the following topologies are investigated: LEV, ERI, CHA, AFX, SFW, AEI, DDR, RTH, ITE, SAV, LTA, RHO, KFI and UFI. The previous observation that light olefin product distributions from a series of small pore, cage-containing zeolites can be classified into four structural categories is further supported by the results shown here from zeolite structures not investigated in the previous study and SAPO and MAPO materials with isostructural frameworks to all the zeolites. Additionally, these data reveal that light olefin product distributions are essentially the same over a given topology independent of framework composition. In order to develop a structure-property relationship between the framework topology and the MTO light olefin product distribution, the concept of the cage-defining ring size is introduced. The cage-defining ring size is defined as the minimum number of tetrahedral atoms of the ring encircling the center of the framework cages in the molecular sieve topology. It is shown that the cage-defining ring size correlates with MTO light olefin product distribution.

This work studies the effects of microscopic shape, crystallinity, and purity for the chemical reaction of CuO nanoparticles with hydrogen sulfide (H 2 S) to form copper sulfide. Several CuO nanomaterials were prepared via various synthesis techniques, including sol-gel, precipitation, hydrothermal synthesis in the presence of a polymer/surfactant, hydrolysis, and electrospinning, using different copper precursors (nitrate and acetate) and thermal treatment conditions (623 to 1023 K). The synthesized materials, which had different morphologies (flower-like, nanobelt-like, petal-like, spherical, and nanofibers) and physiochemical chemical properties (e.g., crystallite size, surface area and pore volume), were tested for their performance as low-temperature H 2 S sorbents in fixed-bed experiments at 294 K and 1 atm. Despite ostensible differences between the various properties of the tested sorbents, a strong linear relationship was recognized between the sorbents' sulfur removal capacity and crystallite size, independent of changes in the materials' microscopic shape and porosity. Specifically, it was observed that CuO materials with crystallite sizes larger than 26 nm exhibited low sulfur uptake capacities (less than 0.5 wt%) whereas capacity increased linearly (from 0.5 wt% to 12 wt%) with decreasing crystallite sizes for materials with CuO crystallites from 26 nm to 5 nm. In addition, the effect of residual carbon on CuO surfaces was also probed in this study, for the first time, showing that amorphous carbon inherently imparted by the use of a polymer, Polyvinylpyrrolidone (PVP) or poly(ethylene oxide) (PEO), or a surfactant, Poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (P123), in the synthesis procedure inhibits reaction and deleteriously impacts the H 2 S uptake capacity. This trend demonstrates that sorption capacity is strongly influenced by crystallite size and is independent of microscopic shape, surface area and mesopore structure. First principles atomistic simulations explain which surface O anions are most reactive and supportive to the observations.

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Thermally stable metal oxide additives within CaO-based sorbents mitigate particulate agglomeration during carbonation–regeneration cycling leading to significant increases in stability.