Pd掺杂Fe催化剂上愈创木酚加氢脱氧理论研究

通过密度泛函理论(DFT)计算研究了愈创木酚在Fe(211)表面上的吸附活化行为和加氢脱氧(HDO)反应性能.讨论了Pd的掺杂和H_2O~*的参与对Fe催化剂活性和选择性的影响.计算结果表明,通过苯环水平吸附在催化剂表面的愈创木酚的稳定性高于仅通过羟基的垂直吸附构型,这有利于苯环, C_(Ar)-OCH_3键和O-CH_3键的活化.在Fe(211)表面上,愈创木酚通过脱甲基再加氢生成邻苯二酚在动力学上比通过脱甲氧基生成苯酚和通过脱羟基生成苯甲醚更有利. Pd掺杂对愈创木酚的吸附稳定性影响较小(0.05 eV),但增加了其加氢脱氧反应的活化能垒,抑制了C_(Ar)-OCH_3, O-CH_3和C_(Ar)-OH键的断裂以及随后加氢生成苯酚,邻苯二酚和苯甲醚的反应过程.在Fe(211)表面上, H_2O~*通过与-CH_3形成氢键作用(H-bonding机理)对反应产生影响,从而降低了愈创木酚脱甲基和脱甲氧基反应的活化能垒.在Fe(211)-1Pd表面上, H_2O~*通过H转移参与反应(H-shuttling机理),促进了愈创木酚向邻苯二酚和苯酚产物的转化,并提高了加氢脱氧反应对苯酚的选择性.

A Theoretical Study on Hydrodeoxygenation of Guaiacol over Pd-Doped Fe Catalyst

The adsorption behavior and hydrodeoxygenation (HDO) property of guaiacol on the Fe(211) surface were studied by density functional theory (DFT) calculations. The effect of Pd doping and the participation of H2O* on the activity and selectivity of Fe catalyst were further investigated. The calculation results showed that guaiacol adsorbed onto the catalyst surface through benzene ring was energetically more stable than adsorbing through solely the hydroxyl group. This favorable adsorption configuration was beneficial to the activation of benzene ring, CAr-OCH3 bond and O-CH3 bond of guaiacol. On Fe(211), catechol formation via demethylation was kinetically more favorable than phenol formation via demethoxylation and anisole formation via dehydroxylation. Pd doping had little effect on the adsorption of guaiacol (<0.05eV), but it increased the energy barriers of guaiacol hydrodeoxygenation, inhibiting the cleavage of CAr-OCH3, O-CH3 and CAr-OH bonds and subsequent hydrogenation to produce phenol, catechol and anisole. On Fe(211), H2O* affected the reaction by forming hydrogen bond interaction with -CH3 group (H-bonding mechanism) to decrease the demethylation and demethoxylation barrier of guaiacol. While on Fe(211)-1Pd, H2O* participated in the H-transfer process (H-shuttling mechanism), promoting the demethoxylation and demethylation of guaiacol and enhancing the relative selectivity to phenol product.