Temperature dependence of aqueous-phase phenol adsorption on Pt and Rh
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RESEARCH ARTICLE
Temperature dependence of aqueous‑phase phenol adsorption on Pt and Rh James Akinola1,2 · Nirala Singh1,2 Received: 13 October 2020 / Accepted: 4 November 2020 © Springer Nature B.V. 2020
Abstract Condensed/aqueous phase surface reactions such as electrocatalytic hydrogenation of bio-oil often involve reactant adsorption and displacement of adsorbed solvent molecules. The enthalpy and entropy of these adsorption processes will influence the kinetics of surface reactions in the condensed/aqueous phase. The value of the adsorption entropy will have a significant effect on how the reactant coverages vary as a function of temperature. Here, adsorption isotherms from 10 to 40 °C and van’t Hoff plots were constructed to directly extract the adsorption entropy and enthalpy of phenol, a bio-oil model compound, on Pt and Rh in aqueous media. We show that the effective adsorption entropy of phenol on Pt and Rh in aqueous phase is positive, in contrast to the negative entropy expected in gas phase. The positive entropy values in the aqueous phase are consistent with adsorbed water gaining a fraction of the entropy of bulk liquid water upon displacement by adsorbed phenol. Consequently, the phenol surface coverage is less dependent on temperature in the aqueous phase compared to the gas phase. The results here give insight to the way in which temperature impacts reaction rates for aqueous-phase phenol hydrogenation reaction.
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10800-020-01503-3) contains supplementary material, which is available to authorized users. Extended author information available on the last page of the article
13
Vol.:(0123456789)
Journal of Applied Electrochemistry
Graphic abstract
Keywords Electrocatalysis · Electrochemical adsorption · Electrocatalytic hydrogenation · Adsorption entropy
1 Introduction Electrochemical conversion of biomass has been proposed as a method to convert waste to value-added streams, with numerous examples of model compounds being converted through electrocatalytic hydrogenation [1–11]. Technoeconomic analyses show that achieving high turnover frequencies at low overvoltages is necessary for an economically feasible process [12]. Reaching these high turnover frequencies at low overvoltages requires developing new electrocatalysts and understanding how to control reaction conditions, such as temperature, to obtain the desired rates. For gas-phase catalytic reactions, the temperature dependence of reaction rates can be understood through the intrinsic activation barrier as well as the adsorption thermodynamics of the reacting species and possible poisoning species [13]. This understanding of gas-phase catalytic reactions allows greater control and reactor design of these systems, as new sets of experiments are not needed for every new temperature or reactant concentration. Instead, the rates can be predicted using models that describe the coverages and rate constants as a function of reaction condit
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