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首页> 外文期刊>Catalysis science & technology >In situ FTIR spectroscopy to unravel the bifunctional nature of aromatics hydrogenation synergy on zeolite/metal catalysts
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In situ FTIR spectroscopy to unravel the bifunctional nature of aromatics hydrogenation synergy on zeolite/metal catalysts

机译：原位FTIR光谱法阐明了在沸石/金属催化剂上芳香族氢的双功能性质

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摘要

Acid sites, in particular Brønsted sites, are often reported to enhance the catalytic performance of metal catalysts, like platinum, in hydrogenation. The significant boost in catalytic performance suggests that a bifunctional mechanism takes place under such conditions. Therefore, aiming to unravel the mechanism behind the synergy effect in the hydrogenation reaction observed on bifunctional zeolite/metal catalysts, the hydrogenation of pyridine adsorbed on *BEA (HBEA) and γ-Al2O3 (Al2O3 – A) promoted by platinum at low pressure, i.e., P ≤ 150 mbar was investigated. The hydrogenation reaction was followed by FTIR spectroscopy aiming to identify the different phenomena linked to pyridine coordinated on Lewis (PyL) and protonated on Brønsted sites (PyH+), the formation of the reaction products, and modifications on the catalyst. Three series of catalysts with different levels of intimacy between the active sites, an important parameter for bifunctional reactions, were used: PtHBEA < PtA + HBEA < PtA|HBEA ≈ PtAl2O3 ≈ ∞. The experimental results indicate a link between the enhanced hydrogenation activity and the intimacy between zeolites acid sites and the metal sites. The lack of desorption of pyridine and piperidine from HBEA during the reaction clearly indicates that the diffusing hydrogen species, i.e., HSP, are responsible for the conversion of pyridine adsorbed on HBEA acid sites. Indeed, a larger diffusion length between Pt and zeolite led to a slower conversion of the adsorbed pyridine, indicating that a bifunctional mechanism is at play. Hence, when the zeolite and metal are in close proximity a hydrogenation mechanism, complementary to the standard metal hydride and involving HSP and an adsorbed unsaturated molecule, occurs leading to an enhanced catalytic performance.
机译：通常据报道，酸性位点，特别是布朗斯特德部位，以增强氢化中金属催化剂（如铂）等金属催化剂的催化性能。催化性能的显着提升表明，双功能机制在这种情况下发生。因此，旨在阐明在双功能沸石/金属催化剂上观察到的协同作用背后的机制，吡啶的氢化吸附在 *BEA（HBEA）和γ-AL2O3（AL2O3 - A）上，在低压下由Platinum促进，低压力，即，研究了p≤150mbar。氢化反应之后是FTIR光谱法，旨在鉴定与在刘易斯（Lewis）（PYL）协调的吡啶相关的不同现象，并在Brønsted位点（PYH+）上进行质子化，形成反应产物的形成和催化剂上的修饰。使用了三个具有不同水平的活动位点的催化剂，使用了双功能反应的重要参数：pthbea

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