The xylene isomers p-xylene, o-xylene, and m-xylene are aromatic hydrocarbons comprising with two methyl groups located at different positions on a benzene ring. The mixture originates from catalytic reforming of crude oil, and each individual isomer acts as a valuable intermediate; however, similar physicochemical properties make their separation difficult. This Review focuses on materials employed for their separation, such as metal−organic frameworks, molecular sieves, organics, and graphene quantum dots. Recent advances in separation of xylene isomers are summarized, including adsorption, membrane, and chromatographic separation techniques, and adsorption capacity and selectivity combined with mechanisms of separation are discussed.

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Zeolites are usually considered to be acid catalysts, which are prone to deactivation due to the coke deposition in the hydrocarbon conversions such as methanolto-olefins (MTO) reaction. Herein, a high-pressure MTO process with cofeeding H 2 and H 2 O is reported, which can effectively prolong the catalytic lifetime of SAPO-34. The corresponding methanol handling capacity is about 200 times larger than that under the normal-pressure condition. Investigation reveals that the ultralong lifetime originates from the hydrogenation ability of the acid sites on SAPO-34 for aromatic species, which can hydrogenate the heavy aromatic deposits (especially the phenanthrene composed of three benene rings) to active aromatic intermediates (methylbenzenes and methylnaphthalenes) and thus slow down the evolution of coke species. A positive synergistic effect between H 2 and H 2 O on prolonging the catalyst lifetime is observed at higher H 2 O partial pressure, likely resulting from the reduced barriers of hydrogenation reactions in the presence of H 2 O. Furthermore, the evolution pathways of coke species are markedly affected by reaction temperature, and fast deactivation may occur below 400 °C due to the formation of large molecule diadamantanes.

Topology and porosity control of Zr6-based MOFs was achieved by introducing steric functionalization into the conformations of substituted tetracarboxylate linkers.

Photoreduction of CO 2 to C 2 + solar fuel is a promising carbon-neutral technology for renewable energy. This strategy is challenged by its low productivity due to low efficiency in multielectron utilization and slow CÀ C coupling kinetics. This work reports a dualmetal photocatalyst consisting of atomically dispersed indium and copper anchored on polymeric carbon nitride (InCu/PCN), on which the photoreduction of CO 2 delivered an excellent ethanol production rate of 28.5 μmol g À 1 h À 1 with a high selectivity of 92 %. Coupled experimental investigation and DFT calculations reveal the following mechanisms underpinning the high performance of this catalyst. Essentially, the InÀ Cu interaction enhances the charge separation by accelerating charge transfer from PCN to the metal sites. Indium also transfers electrons to neighboring copper via CuÀ NÀ In bridges, increasing the electron density of copper active sites. Furthermore, InÀ Cu dual-metal sites promote the adsorption of *CO intermediates and lower the energy barrier of CÀ C coupling.

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Understanding the structure–catalytic activity relationship is crucial for developing new catalysts with desired performance. In this contribution, we report the performance of In2O3 with different crystal phases in the reverse water gas shift (RWGS) reaction, where we observe changing activity induced by a phase transition under reaction conditions. Cubic In2O3 (c-In2O3) exhibits a higher RWGS rate than the hexagonal phase (h-In2O3) at temperatures below 350 °C because of its (1) enhanced dissociative adsorption of H2, (2) facile formation of the oxygen vacancies, and (3) enhanced ability to adsorb and activate CO2 on the oxygen vacancies, as suggested both experimentally and computationally. Density functional theory results indicate that the surface oxygen arrangement on the cubic polymorph is key to rapid H2 adsorption, which facilitates oxygen vacancy formation and subsequent CO2 adsorption to yield high RWGS reactivity. At 450 °C and above, the activity of h-In2O3 increases gradually with time on stream, which is caused by a phase transition from h-In2O3 to c-In2O3. In situ X-ray diffraction experiments show that h-In2O3 is first reduced by H2 and subsequently oxidized by CO2 to c-In2O3. These findings highlight the importance of the crystal phase in the catalytic RWGS reaction and provide a new dimension for understanding/designing RWGS catalysts.

Zr6-based metal–organic frameworks (MOFs) with tetratopic organic linkers have been extensively investigated owing to their versatile structural tunability. While diverse topologies and polymorphism in the resulting MOFs are often encountered with tetratopic linkers and Zr6 nodes, reports on phase transitions within these systems are rare. Thus, we have a limited understanding of polymorph transformations, hindering the rational development of pure phase materials. In this study, a phase transition from a microporous MOF, scu-NU-906, to a mesoporous MOF, csq-NU-1008, was discovered and monitored through in situ variable temperature liquid-cell transmission electron microscopy (VT-LCTEM), high-resolution transmission electron microscopy (HRTEM), and in situ variable temperature powder X-ray diffraction (VT-PXRD). It was found that the microporous- to-mesoporous transformation in the presence of formic acid occurs via a concomitant dissolution–reprecipitation process.