Relationships between the Hydrogenation and Dehydrogenation Properties of Rh‑, Ir‑, Pd‑, and Pt-Containing Zeolites Y Studied by In Situ MAS NMR Spectroscopy and Conventional Heterogeneous Catalysis

The intrinsic hydrogenation activities of homologous series of noble-metal-containing zeolites Y were studied by in situ solid-state NMR spectroscopy under semibatch conditions. For the hydrogenation of acrylonitrile, reaction rates in the sequence Pd/H,Na–Y > Rh/H,Na–Y > Pt/H,Na–Y > Ir/H,Na–Y were determined. The dehydrogenation of propane at these zeolites gave a sequence of the turnover frequencies of Ir/H,Na–Y > Rh/H,Na–Y > Pd/H,Na–Y, while Pt/H,Na–Y zeolites showed significantly higher activities. The temperature-programmed desorption of hydrogen (H₂-TPD) was utilized for studying the strength of H₂/metal interactions. The positions of the high-temperature peaks were arranged according to 2.8Pd/H,Na–Y (723 K) > 2.3Rh/H,Na–Y (713 K) > 4.7Ir/H,Na–Y (663 K). Comparison of these data indicates that strong H₂/metal interactions are accompanied by a preferred formation of surface hydrogen atoms, which are the reason for the high hydrogenation activity of Pd/H,Na–Y zeolites compared with Rh/H,Na–Y and Ir/H,Na–Y zeolites. In the case of the propane dehydrogenation, the strong H₂/Pd interactions in Pd/H,Na–Y zeolites hinder the desorption of the reaction product H₂, explaining the lower dehydrogenation activity of these zeolites compared with Rh/H,Na–Y and Ir/H,Na–Y zeolites. For the high catalytic activities of the Pt/H,Na–Y zeolites, an effect of strongly chemisorbed hydrogen atoms inside the Pt clusters is discussed

Relationships between the Hydrogenation and Dehydrogenation Properties of Rh‑, Ir‑, Pd‑, and Pt-Containing Zeolites Y Studied by In Situ MAS NMR Spectroscopy and Conventional Heterogeneous Catalysis

The intrinsic hydrogenation activities of homologous series of noble-metal-containing zeolites Y were studied by in situ solid-state NMR spectroscopy under semibatch conditions. For the hydrogenation of acrylonitrile, reaction rates in the sequence Pd/H,Na–Y > Rh/H,Na–Y > Pt/H,Na–Y > Ir/H,Na–Y were determined. The dehydrogenation of propane at these zeolites gave a sequence of the turnover frequencies of Ir/H,Na–Y > Rh/H,Na–Y > Pd/H,Na–Y, while Pt/H,Na–Y zeolites showed significantly higher activities. The temperature-programmed desorption of hydrogen (H₂-TPD) was utilized for studying the strength of H₂/metal interactions. The positions of the high-temperature peaks were arranged according to 2.8Pd/H,Na–Y (723 K) > 2.3Rh/H,Na–Y (713 K) > 4.7Ir/H,Na–Y (663 K). Comparison of these data indicates that strong H₂/metal interactions are accompanied by a preferred formation of surface hydrogen atoms, which are the reason for the high hydrogenation activity of Pd/H,Na–Y zeolites compared with Rh/H,Na–Y and Ir/H,Na–Y zeolites. In the case of the propane dehydrogenation, the strong H₂/Pd interactions in Pd/H,Na–Y zeolites hinder the desorption of the reaction product H₂, explaining the lower dehydrogenation activity of these zeolites compared with Rh/H,Na–Y and Ir/H,Na–Y zeolites. For the high catalytic activities of the Pt/H,Na–Y zeolites, an effect of strongly chemisorbed hydrogen atoms inside the Pt clusters is discussed

Effect of <i>n</i>‑Butanol Cofeeding on the Methanol to Aromatics Conversion over Ga-Modified Nano H‑ZSM‑5 and Its Mechanistic Interpretation

Ga-modified nano H-ZSM-5 zeolites with different Ga contents were prepared and applied as methanol-to-aromatics (MTA) catalysts. The Ga introduction can strongly increase the selectivity to aromatics but also decrease the catalyst lifetime simultaneously. Upon the cofeeding of <i>n</i>-butanol with methanol, a significant prolongation of the catalyst lifetime from 18 to ca. 50 h can be achieved. According to several spectroscopic results, e.g., TGA, GC–MS, in situ UV/vis, and solid-state MAS NMR spectroscopy, the addition of <i>n</i>-butanol during the MTA conversion shows no impact on the deactivation mechanism but can influence the dual-cycle mechanism. Namely, <i>n</i>-butanol preferentially adsorbs on Brønsted acid sites over methanol, followed by dehydration into <i>n</i>-butene. The formed <i>n</i>-butene can directly participate in the olefin-based cycle and, therefore, significantly alter the proportions of the dual-cycle mechanism. These results provide mechanistic insights into the roles of <i>n</i>-butanol cofeeding in the MTA conversion and exemplify a simple but efficient strategy to prolonged the catalyst lifetime, which is crucial to the industrial application