It has been found in recent years that H-ITQ-13 zeolite as a catalyst performs excellently in the conversion of methanol to olefins (MTO); however, the relationship between the catalytic performance and its unique pore structure remains rather ambiguous. In this work, the reaction mechanism of MTO over H-ITQ-13 was investigated by density functional theory considering dispersive interactions (DFT-D). The results illustrate that both the aromatic and alkene cycles are viable for MTO over H-ITQ-13. Via the aromatic cycle, the selectivity to ethene is higher than that to propene (with pentamethylbenzene (5MB) and 1,4-dimethylnaphthalene (2MN) as the active hydrocarbon pool (HCP) species), whereas via the alkene cycle (with lower alkenes as the HCP species), propene is the primary product. The alkene cycle takes priority over the aromatic cycle, since the transition states formed in the alkene cycle can be well stabilized in the three-dimensional framework of small pores in H-ITQ-13; as a result, high selectivity to propene can be achieved for MTO over H-ITQ-13. The insights shown in this work help to clarify the reaction mechanism of MTO over H-ITQ-13 and reveal the relationship between the catalytic performance and the unique pore structure of H-ITQ-13, which is of great benefit to the development of better MTO catalysts and reaction processes with high selectivity to propene.

The treatment of phenolic-containing wastewater has received increased attention in recent years. In this study, the N-doped porous carbons were prepared from lignite with tripolycyanamide as the N source, and their phenol adsorption behaviors were investigated. Results clearly showed that the addition of tripolycyanamide largely improved the surface area, micropore volume, N content and thus the phenol adsorption capacity of lignite-based carbons. The N-doped sample prepared at 700 °C showed a surface area of 1630 m²/g and a phenol adsorption capacity as high as 182.4 mg/g at 20 °C, which were 2.0 and 1.6 times that of the lignite-based carbon without N-doping. Pseudo-second order and Freundlich adsorption isotherm models could better explain the phenol adsorption behaviors over lignite-based N-doped porous carbon. Theoretical calculations demonstrated that phenol adsorption energies over graphitic-N (−72 kJ/mol) and pyrrolic-N (−74 kJ/mol) groups were slightly lower than that over the N-free graphite layer (−71 kJ/mol), supporting that these N-containing groups contribute to enhance the phenol adsorption capacity. The adsorption mechanism of phenol over porous carbon might be interpreted by the π–π dispersion interactions between aromatic-ring and carbon planes, which could be enhanced by N-doping through increasing π electron densities in the carbon plane.

A series of Pd/SiO₂ catalysts were prepared with different Pd precursors by a dry ball-milling method and used in the catalytic oxidation of lean methane at low temperature. The effect of Pd precursors on the catalytic performance was investigated and the state of the most active Pd species was probed. The results indicate that dry ball-milling is a simple but rather effective method to prepare the Pd/SiO₂ catalysts for lean methane oxidation, and palladium acetylacetonate is an ideal precursor to obtain a highly active Pd/SiO₂-Acac catalyst with well- and stably dispersed Pd species, owing to the tight contact between acetylacetonate and Si–OH on the SiO₂ support. Besides the size and dispersion of Pd particles, the oxidation state of Pd species also plays a crucial role in determining the catalytic activity of Pd/SiO₂ in lean methane oxidation at low temperature. A non-monotonic dependence of the catalytic activity on the Pd oxidation state is observed. The activity of various Pd species follows the order of PdO_x >> Pd > PdO; the PdO_x/SiO₂-Acac catalysts (in particular for PdO_0.82/SiO₂-Acac when x = 0.82) exhibit much higher activity in lean methane oxidation at low temperature than Pd/SiO₂-Acac and PdO/SiO₂-Acac. The catalytic activity of PdO_x/SiO₂ may degrade during the methane oxidation due to the gradual transformation of PdO_x to PdO in the oxygen-rich ambiance; however, such degradation is reversible and the activity of a degraded Pd/SiO₂ catalyst can be recovered through a redox treatment to regain the PdO_x species. This work helps to foster a better understanding of the relationship between the structure and performance of supported Pd catalysts by clarifying the state of active Pd species, which should be beneficial to the design of an active catalyst in lean methane oxidation at low temperature.