Bifunctional Zn–Y/Beta catalyst was applied in the reaction mechanism study of the ethanol to butadiene conversion to clarify the roles of Zn and Y functional sites in each individual reaction step. According to the results of several complementary methods, i.e., ethanol temperature-programmed desorption (TPD), temperature-programmed surface reaction (TPSR), and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), the reaction network consisting of several key steps, i.e., ethanol dehydrogenation, acetaldehyde aldol condensation, and crotonaldehyde reduction, was elucidated. An enolization mechanism was verified to involve in the coupling step. During this reaction, the Lewis acidic Zn and Y species in [Si]­Beta zeolite were both active in the ethanol dehydrogenation, aldol condensation, and Meerwein–Ponndorf–Verley reduction. In this cycle, Zn species exhibited the higher dehydrogenation activity but lower coupling activity than that of Y species. Through the combination of the two species in one catalyst, i.e., Zn–Y/Beta, the synergistic effect of the bifunctional sites could be achieved. Our study provides mechanistic insights into the cascade transformation of ethanol to butadiene and the fundamental guidelines for the rational design of eligible catalysts for the reaction.

Acetone‐2‐13C, trimethylphosphine oxide (TMPO), and ammonia were applied as probe molecules for solid‐state NMR investigations of Lewis acid sites on γ‐Al2O3, TiO2/anatase, and lithium‐exchanged zeolite Na‐Y. An indication for Lewis acid sites are the 31P MAS NMR signals at 48–51 ppm for TMPO‐loaded catalysts. The determination of the Lewis site density through the evaluation of these 31P MAS NMR signals, however, is difficult owing to the demanding TMPO adsorption procedure. Upon ammonia adsorption, the formation of ammonium ions at Brønsted acid sites and the coordination of ammonia at Lewis acid sites cause 1H MAS NMR signals at 6–7 ppm and −0.5–3 ppm, respectively. The integration of these signals results in the densities of Brønsted and Lewis acid sites. Future studies have to clarify whether the different 1H chemical shifts in the range of −0.5–3 ppm for ammonia coordinated at Lewis acid sites on solid catalysts are a hint at the different strengths of these surface sites.

We have studied both theoretically and experimentally the optical pumping of Cs atoms trapped in ͑bodycentered-cubic and hexagonal-close-packed͒ crystalline 4 He matrices. The theoretical approach is based on rate equations for which time-dependent and asymptotic solutions are obtained in the case of depopulation and repopulation pumping. Comparison with experiments show that repopulation pumping, i.e., a process in which spin polarization in the excited state is not destroyed, is the dominant pumping mechanism in both crystalline phases.

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