Surfactant-free mixed-metal hydroxide water oxidation nanocatalysts were synthesized by pulsed-laser ablation in liquids. In a series of [Ni-Fe]layered double hydroxides with intercalated nitrate and water, [Ni 1−x Fe x (OH) 2 ](NO 3 ) y (OH) x−y •nH 2 O, higher activity was observed as the amount of Fe decreased to 22%. Addition of Ti 4+ and La 3+ ions further enhanced electrocatalysis, with a lowest overpotential of 260 mV at 10 mA cm −2 . Electrocatalytic water oxidation activity increased with the relative proportion of a 405.1 eV N 1s (XPS binding energy) species in the nanosheets.

SSZ-13 materials have been synthesized with varying amounts of Al to produce samples with different concentrations of Brønsted acid sites, and consequently, these SSZ-13 materials contain increasing numbers of paired Al heteroatoms with increasing Al content. These materials were then characterized and tested as catalysts for the methanol-to-olefins (MTO) reaction at 400 °C and 100% methanol conversion under atmospheric pressure. A SAPO-34 sample was also synthesized and tested for comparison. SSZ-13 materials exhibited significant differences in MTO reactivity as Si/Al ratios varied. Reduced Al content (higher Si/Al ratio) and, consequently, fewer paired Al sites led to more stable light olefin selectivities, with a reduced initial transient period, lower initial propane selectivities, and longer catalyst lifetime. To further support the importance of paired Al sites in the formation of propane during this initial transient period, a series of experiments was conducted wherein an H-SSZ-13 sample was exchanged with Cu2+, steamed, and then back-exchanged to the H form. The H-SSZ-13 sample exhibited high initial propane selectivity, while the steamed H-SSZ-13, the Cu2+-exchanged SSZ-13 sample, and the steamed Cu-SSZ-13 sample did not, as expected since steaming selectively removes paired Al sites and Cu2+ exchanges onto these sites. However, when it was back-exchanged to the proton form, the steamed Cu-SSZ-13 sample still exhibited the high initial alkane selectivity and transient period typical of the higher Al content materials. This is attributed to protection of paired Al sites during steaming via the Cu2+ cation. Post-reaction coke analyses reveal that the degree of methylation for each aromatic species increases with increasing Si/Al in SSZ-13. Further, SAPO-34 produces more polycyclic species than SSZ-13 samples. From these data, the paired Al site content appears to be correlated with both MTO reaction behavior and coke species formation in SSZ-13 samples.

Zeolite SSZ-39 is evaluated for catalyzing the methanol-to-olefins (MTO) reaction. By steaming NH4–SSZ-39, Al can be removed from framework positions, resulting in an increase in framework-Si/AlT and thus a lowered active acid site density. The Si/AlT ratios can be controlled by the steaming temperatures. SSZ-39 steamed at 750 °C, with preserved pore volume and morphology, is an excellent MTO catalyst, as high, stable olefin selectivities, long time-on-stream activity, and low alkane production are observed. Moreover, interesting propylene/ethylene/butylene ratios of 2.8/1/1.1 are obtained, likely related to the shape of the AEI cage. By Cu2+-exchanging SSZ-39, evidence is provided to show that AlT sites in close proximity (high AlT density) produce the unwanted effects (higher alkane-make and carbonaceous deposits) in nonsteamed materials during MTO.

Zeolite A (LTA) has many large-scale uses in separations and ion exchange applications. Because of the high aluminum content and lack of high-temperature stability, applications in catalysis, while highly desired, have been extremely limited. Herein, we report a robust method to prepare pure-silica, aluminosilicate (product Si/Al = 12–42), and titanosilicate LTA in fluoride media using a simple, imidazolium-based organic structure-directing agent. The aluminosilicate material is an active catalyst for the methanol-to-olefins reaction with higher product selectivities to butenes as well as C5 and C6 products than the commercialized silicoalumniophosphate or zeolite analogue that both have the chabazite framework (SAPO-34 and SSZ-13, respectively). The crystal structures of the as-made and calcined pure-silica materials were solved using single-crystal X-ray diffraction, providing information about the occluded organics and fluoride as well as structural information.

Chabazite (CHA)-type zeolites are prepared from the hydrothermal conversion of faujasite (FAU)-type zeolites, dealuminated by high-temperature steam treatments (500−700°C), and evaluated as catalysts for the methanol-to-olefins (MTO) reaction. The effects of temperature and partial pressure of water vapor during steaming are investigated. Powder X-ray diffraction (XRD) and Ar physisorption data show that the steam treatments cause partial structural collapse of the zeolite with the extent of degradation increasing with steaming temperature. 27 Al MAS NMR spectra of the steamed materials reveal the presence of tetrahedral, pentacoordinate, and octahedral aluminum. NH 3 and i-propylamine temperature-programmed desorption (TPD) demonstrate that steaming removes Brønsted acid sites, while simultaneously introducing larger pores into the CHA materials that make the remaining acid sites more accessible. Acid washing the steamed CHA-type zeolites removes a significant portion of the extra-framework aluminum, producing an increase in the bulk Si/Al ratio as well as the adsorption volume. The proton form of the as-synthesized CHA (Si/Al = 2.4) rapidly deactivates when tested for MTO at a reaction temperature of 400°C and atmospheric pressure. CHA samples steamed at 600°C performed the best among the samples tested, showing increased olefin selectivities as well as catalyst lifetime compared to the unsteamed CHA. Both lifetime and C 2 −C 3 olefin selectivities are found to increase with increasing reaction temperature. At 450°C, CHA steamed at 600°C reached a combined C 2 −C 3 olefin selectivity of 74.2% at 100% methanol conversion, with conversion remaining above 80% for more than 130 min of time-on-stream (TOS) before deactivating. More stable time-on-stream behavior is observed for 600°C-steamed CHA that underwent acid washing: conversion above 90% for more than 200 min of TOS at 450°C with a maximum total C 2 −C 3 olefin selectivity of 71.4% at 100% conversion.