Aqueous phase hydrogenation of phenol catalyzed by Pd and PdAg on ZrO2

• Published in: Applied catalysis. A, General Vol. 548; pp. 128 - 135
• Main Authors: Resende, Karen A., Hori, Carla E., Noronha, Fabio B., Shi, Hui, Gutierrez, Oliver Y., Camaioni, Donald M., Lercher, Johannes A.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 25.11.2017
• ISSN: 0926-860X; 1873-3875
• DOI: 10.1016/j.apcata.2017.08.005

[Display omitted] •The turnover frequency (TOF) increases with the Pd particle size.•The surface coverages of phenol and H2 higher on 0.5% Pd/ZrO2.•The activation energy was lowest on the least active sample (0.5% Pd/ZrO2).•0.5%Pd/ZrO2 had unfavorable activation entropies caused for the strongly bound in the small species.•The presence of Ag increases considerably the TOF of the reaction by decreasing the Ea and increasing the coverages of phenol and H2. The impact of particle size of ZrO2-supported Pd and of alloying with Ag was explored for hydrogenation of phenol in aqueous phase. Kinetic assessments were performed in a batch reactor, on monometallic Pd/ZrO2 samples with different Pd loadings (0.5%, 1% and 2%), as well as on a 1% PdAg/ZrO2 sample. The catalytic activity normalized to accessible Pd (turnover frequency, TOF) increased with the particle size of Pd. Reaction orders in phenol and H2 and lower activation energies suggest that smaller particles bind the reacting substrates more strongly, leading to higher surface coverages by phenol. However, surprisingly, smaller Pd particles exhibited lower TOFs. The lower activity of the small Pd particles is attributed to lower activation entropies for the strongly bound species. The presence of Ag increased the catalyst activity by decreasing the apparent energy of activation and increasing the coverages of phenol and H2, without negatively affecting the activation entropy.