is widely used for catalyzing various reactions, and its performance depends on the valence state, morphology and dispersion of Ag species. However, detailed anchoring mechanism of Ag species on γ-Al 2 O 3 remains largely unknown. Herein, we reveal that the terminal hydroxyls on γ-Al 2 O 3 are responsible for anchoring Ag species. The abundant terminal hydroxyls existed on nanosized γ-Al 2 O 3 can lead to single-atom silver dispersion, thereby resulting in markedly enhanced performance than the Ag cluster on microsized γ-Al 2 O 3 . Density-functional-theory calculations confirm that Ag atom is mainly anchored by the terminal hydroxyls on (100) surface, forming a staple-like local structure with each Ag atom bonded with two or three terminal hydroxyls. Our finding resolves the puzzle on why the single-atom silver dispersion can be spontaneously achieved only on nanosized γ-Al 2 O 3 , but not on microsized γ-Al 2 O 3 . The obtained insight into the Ag species dispersion will benefit future design of more efficient supported Ag catalysts.

A unique insight into the acidic nature of the tri-coordinated framework aluminum (AlFR) in H-ZSM-5 zeolite catalysts has been provided using multi-nuclear and multi-dimensional solid-state NMR spectroscopy in conjunction with TMPO probe molecules.

The accurate characterization of the acid strength of zeolites is of great importance to understand their catalytic performance and the rational design of highly efficient zeolite catalysts. The 31 P MAS NMR spectroscopy of adsorbed trimethylphosphine oxide (TMPO) technique has been widely employed to measure the acid strength of various solid acid catalysts. Here, the influence of TMPO loading on characterizing the zeolite acidity is explored by using two-dimensional (2D) hetero-and homonuclear correlation NMR experiments combined with density functional theory calculations. It is found that the TMPO loading plays a crucial role in the accurate measurement of zeolite acid strength. Saturated adsorption of TMPO molecules (P/Al = 1.0) can result in the formation of a TMPO dimer on one Brønsted acid site (BAS), which will conceal the acid strength of the specific acid site if it is merely based on 31 P chemical shifts in the 1D spectrum. This is further confirmed by 2D 31 P{ 1 H} heteronuclear correlation (HETCOR) and 31 P− 31 P double-quantum (DQ) homonuclear correlation experiments on TMPO-loaded ZSM-5 zeolites. By carefully controlling the amount of TMPO adsorption, such as low or medium TMPO loadings (i.e., P/Al = 0.2 or P/Al = 0.4), the 31 P chemical shift can not only accurately reflect the BAS strength of the zeolite, but also can discriminate the Brønsted and Lewis acid sites due to well-resolved 2D 31 P{ 1 H} HETCOR NMR. The results presented herein provide a strategy to assess the acidity of zeolites more precisely by a TMPO probe molecule, which is helpful for the optimization of catalytic performances of zeolite catalysts.

Crystallization of AlPO4-5 with AFI structure under solvent-free conditions has been investigated. Attention was mainly focused on the characterization of the intermediate phases formed at the early stages during the crystallization. The development in the long-range ordering of the solid phases as a function of crystallization time was monitored by XRD, SEM, IR, UV-Raman, and MAS NMR techniques. Particularly, the UV-Raman spectroscopy was employed to obtain the information on the formation process of the framework. J-HMQC (27)Al/(31)P double-resonance NMR experiments were used to identify the P-O-Al bonded species in the intermediate phases. For the first time the P-O-Al bonded species in the intermediate phases can be correctly described through using this advanced NMR technique. The crystallization under solvent-free conditions appears to follow the pathway: The initial amorphous raw material is converted to an intermediate phase which has four-/six-membered ring species, then gradually transformed into crystalline AlPO4-5. This observation is not consistent with the common idea that the intermediate phase is the semicrystalline intermediates with a three-dimensional structure.

Di-n-propylamine (DPA) molecules induce the transformation from 4/6-MR chains to a 2D layered structure and then to 3D crystals of AlPO4-11 molecular sieves.

High rutile content and low specific surface area of the vanadia-based catalysts contribute to an excellent NH3-SCR activity.

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The decrease of polymeric vanadyl species due to treatment under different atmospheres results in the reduction of NH3-SCR activity.