To improve the stability of MOF catalysts, a design of MOF@mesoporous SiO 2 yolk-shell nanoreactors was developed via a mesoporous silica coating followed by selective water-etching strategy. Benefiting from their permeable mesoporous SiO 2 shells, exposed active sites on MOF surfaces, and protective shells, the yolkshell nanoreactors exhibit higher catalytic stability than bare MOF crystals in CO 2 cycloaddition, with product yield remaining unchanged upon three cycles.
Zeolites are widely used in catalysis, gas separation, ion exchange, etc. due to their superior physicochemical properties, which are closely related to specific features of their framework structures. Although more than two hundred different framework types have been recognized, it is of great interest to explore from a crystallographic perspective, the atomic positions, surface terminations, pore connectivity and structural defects that deviate from the ideal framework structures, namely local structural modulation. In this article, we review different types of local modulations in zeolite frameworks using various techniques, especially electron microscopy (EM). The most recent advances in resolving structural information at the atomic level with aberration corrected EM are also presented, commencing a new era of gaining atomic structural information, not only for all tetrahedral atoms including point vacancies in framework but also for extra‐framework cations and surface terminations.
Among homologous series of metal oxides, Andersson‐Magnéli phases TinO2n‐1 (n=4–10) have attracted renewed scientific attention because of their behaviour in electrical conductivity and chemical/thermal stability. Various applications have also been reported for the phases with different values of n, or slightly reduced rutile (TiO2). The characteristic properties of these materials depend strongly on the compositional deviation from TiO2 and the way in which the structure accommodates the deviation. Thus, an urgent requirement is to overcome difficulties in characterizing such materials at atomic resolution. Here, we trace the discovery of the Andersson‐Magnéli phases, and report the application of recent developments in electron microscopy to reveal the relation, at the local level, between structural characteristics and electronic states, specifically for the materials TinO2n‐1 with n=4–8. The electrical conductivity of Ti4O7 has been reported previously to show three clearly distinct states on decreasing temperature from 300 K. For this reason, we focus on Ti4O7 as a representative example of the TinO2n‐1 phases and report structural characteristics at temperatures corresponding to each of the three different phases, focusing on the distribution of Ti3+ and Ti4+ cations from analysis of single‐crystal XRD data. Electron diffraction experiments and electrical conductivity measurements are also reported.
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