Impact of pretreatment and thiol modifiers on the partial oxidation of glutaraldehyde using Pd/Al2O3
Impact of pretreatment and thiol modifiers on the partial oxidation of glutaraldehyde using Pd/Al2O3
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DOI：
10.1016/j.apcata.2023.119229
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发表时间：
2023-04-29
影响因子：
5.5
通讯作者：
Medlin，J. Will
中科院分区：
文献类型：
--
作者：
Al Khulaifi，Faysal M.;Alsunni，Yousef A.;Medlin，J. Will
生物质衍生化合物的氧化转化为增值化学品是具有挑战性的，因为多官能团反应物有过度氧化的趋势。催化剂的性能对合成条件和预处理条件都很敏感。此外，用自组装单分子膜(SAM)包覆催化剂在调节活性和选择性方面显示出很好的前景。以Pd/Al_2O_3为催化剂，添加和不添加不同的硫代SAM改性剂，研究了戊二醛(GA)液相部分氧化制戊二醛(GSA)的反应。与未处理的催化剂相比，还原处理的催化剂活性提高，表观诱导期缩短。进一步发现GSA的选择性对SAM层的同一性很敏感，亲水性的硫代甘油(TG)和硫代乳酸(TLA)涂层显示出对GSA的选择性的提高；TG涂层将选择性从∼从60%(在未涂层的催化剂和表面涂覆疏水硫醇的催化剂上)提高到∼(相同转化率)的80%(∼为30%)。然而，与UC和疏水涂层材料相比，TG涂层显示出较低的催化速率。各种材料表征技术排除了形态和电子原因。密度泛函理论(DFT)计算表明，与未涂层的Pd表面相比，氢键稳定了对GSA的吸附。然而，也预测了戊二酸(GAC)对TG涂层Pd的吸附的很大稳定性，可能导致这种过氧化产物的积累和较低的总速率。通过实验证实了GAC吸附对GA部分氧化速率的抑制作用。因此，建议寻找更具特异性的稳定氧化程度较低的中间体的方法，以此作为提高反应速度和选择性的策略。
Oxidative conversion of biomass-derived compounds to value-added chemicals is challenging due to the tendency of multi-functional reactants to overoxidize. Catalyst performance can be sensitive to both synthesis and pretreatment conditions. Additionally, coating the catalyst with self-assembled monolayers (SAMs) has shown promise in modulating activity and selectivity. Here, the liquid-phase partial oxidation of glutaraldehyde (GA) to glutaric semialdehyde (GSA) was investigated as a model reaction using a Pd/Al2O3catalyst, with and without various thiolate SAM modifiers. Reductive pretreatment of the catalyst showed enhancement in the activity and a shortening of an apparent induction period relative to the untreated catalyst. The selectivity for GSA was further found to be sensitive to the identity of the SAM layers, with hydrophilic thioglycerol (TG) and thiolactic acid (TLA) coatings showing an enhancement in selectivity to GSA; the TG coating raised selectivity from ∼ 60 % (on uncoated catalyst and catalysts coated with hydrophobic thiols) to ∼ 80 % at identical conversion (∼ 30 %). However, the TG coating exhibited lower catalytic rates compared to UC and hydrophobically coated materials. Morphological and electronic causes were ruled out with various materials characterization techniques. Density functional theory (DFT) calculations suggested that hydrogen bonding stabilizes adsorption of GSA compared to the uncoated Pd surface. However, a large stabilization of glutaric acid (GAC) adsorption for TG-coated Pd was also predicted, likely leading to accumulation of this overoxidation product and lower overall rates. Inhibition of the rate of GA partial oxidation by GAC adsorption was then corroborated experimentally. Finding ways to stabilize the less-oxidized intermediates with more specificity is thus suggested as a strategy to improve rate and selectivity.