Hydrodeoxygenation of Phenol over Pd Catalysts. Effect of Support on Reaction Mechanism and Catalyst Deactivation
Hydrodeoxygenation of Phenol over Pd Catalysts. Effect of Support on Reaction Mechanism and Catalyst Deactivation
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DOI：
10.1021/acscatal.6b02022
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发表时间：
2017-03-01
期刊：
影响因子：
12.9
通讯作者：
Noronha, Fabio B.
中科院分区：
文献类型：
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作者：
de Souza, Priscilla M.;Rabelo-Neto, Raimundo C.;Noronha, Fabio B.
采用固定床反应器，考察了载体类型（SiO2、Al 2 O3、TiO 2、ZrO 2、CeO 2和CeZrO 2）对Pd基催化剂在573 K下苯酚加氢脱氧反应性能的影响。产品的分布受支持类型的影响很大。“a苯是Pd/TiO 2和Pd/ZrO 2上的主要产物;另一方面，环己酮是Pd/SiO 2、Pd/Al 2 O 3、Pd/CeO 2和Pd/CeZrO 2上的主要化合物。通过DRIFTS实验和中间产物的催化实验，提出了苯酚互变异构反应机理。相对于Pd/TiO 2和Pd/ZrO 2催化剂的苯的高选择性可能是由于该载体的亲氧位点，其由紧邻金属颗粒的外围的不完全配位的Ti 4+和Zr 4+阳离子表示。酮基互变异构体中间体中的氧与亲氧位点之间更强的相互作用促进了C=O键的选择性氢化。Pd/SiO2、Pd/Al 2 O3、Pd/TiO 2和Pd/ZrO 2催化剂在TOS期间显著失活。然而，Pd/CeO 2和Pd/CeZrO 2更稳定，并且仅观察到轻微的活性损失。反应后通过拉曼光谱没有检测到碳沉积物。反应条件下的DRIFTS实验揭示了苯氧基和中间体物种在反应过程中的积累。这些物种仍然吸附在刘易斯酸网站，阻止这些网站和抑制进一步的反应物吸附。催化剂失活的主要原因是Pd颗粒尺寸的增大和酸中心密度的降低。Pd/CeO 2和Pd/CeZrO 2催化剂的较高稳定性可能是由于这些载体的较高量的氧空位。
This work investigates the effect of the type of support (SiO2, Al2O3, TiO2, ZrO2, CeO2, and CeZrO2) on the performance of Pd-based catalysts for the hydrodeoxygenation of phenol at 573 K using a fixed-bed a reactor. Product distribution is significantly affected by the type of support." a Benzene was the major product over Pd/TiO2 and Pd/ZrO2; on the other a hand, cyclohexanone was the main compound over Pd/SiO2, Pd/Al2O3, Pd/ CeO2, and Pd/CeZrO2. A reaction mechanism based on the tautomerization of phenol was proposed on the basis of DRIFTS experiments and catalytic tests with the intermediate products. The high selectivity to benzene over Pd/ TiO2 and Pd/Zr02 catalysts is likely due to the oxophilic sites of this support represented by incompletely coordinated Ti4+ and Zr4+ cations in close proximity to the periphery of metal particles. The greater interaction between oxygen in the keto-tautomer intermediate with oxophilic sites promotes the selective hydrogenation of C=O bond. Pd/SiO2, Pd/A1203, Pd/TiO2 and Pd/ZrO2 catalysts significantly deactivated during TOS. However, Pd/CeO2 and Pd/CeZrO2 were more stable, and only slight losses in activity were observed. Carbon deposits were not detected by Raman spectroscopy after reaction. DRIFTS experiments under reaction conditions revealed a buildup of phenoxy and intermediate species during reaction. These species remained adsorbed on the Lewis acid sites, blocking those sites and inhibiting further reactant adsorption. The growth of Pd particle size and the reduction in acid site density during HDO of phenol were the primary routes of catalyst deactivation. The higher stability of Pd/CeO2 and Pd/CeZrO2 catalysts is likely due to the higher amount of oxygen vacancies of these supports.