Performance of Base and Noble Metals for Electrocatalytic Hydrogenation of Bio-Oil-Derived Oxygenated Compounds

Abstract

Electrocatalytic hydrogenation is a particularly attractive approach for converting the most unstable compounds in biogenic feedstocks at ambient conditions without external H2. Here, we synthesized a variety of carbon-supported transition metal catalysts and characterized their activity for the electrocatalytic hydrogenation of a series of model compounds and pyrolysis bio-oil. Carbonyl compounds, especially aromatic aldehydes, such as furfural and benzaldehyde, are particularly inclined to hydrogenation driven by an applied current. This was verified with pure solutions of the model compounds and with pyrolysis bio-oil, where we achieved stable and steady continuous operation on Pd. When optimal catalyst composition was chosen, the conversion of benzaldehyde shifted from alcohol production (e.g., on Pd and Cu) to dimerization (e.g., on Co, Ni, and Zn). Pd and Cu were shown to offer the best compromise between reaction rates and efficiency although, in general, base metals offer similar conversions but better efficiencies than noble metals. Thus, the present work offers foundational results and guidelines for choosing the optimal metal catalyst and the applied potential for processing organic feedstocks as a function of its composition.

Upgrading of Bio‐Oil Model Compounds and Bio‐Crude into Biofuel by Electrocatalysis: A Review

“…Electrode commonly consists of catalysts and conductive material (catalyst support), which has a crucial effect on the bio‐oil conversion and products selectivity in bio‐oil ECH process. In detail, electrocatalysts like noble metal, [32b,33,39b,48] base metal, [32a,48a,c,49] alloy, [9a,50] oxide [51] and phosphide [40a] have been reported for upgrading bio‐crude and model compounds by ECH. Besides, graphite, activated carbon and other porous materials as catalyst supports can improve the electrocatalytic performance.…”

“…Besides, graphite, activated carbon and other porous materials as catalyst supports can improve the electrocatalytic performance. Two types of cathodes are commonly utilized in the ECH system: (i) catalysts‐coated carbon cathodes (e. g., Pd/C/ carbon felt (CF)); [48a] (ii) metal sheets as both the cathode and catalyst [49c] …”

“…Large amounts of noble metals such as Pd, Rh, Ru, Au and Pt have been employed as cathode materials during ECH of aldehyde and phenolic model compounds [28,32b,39b,44b, 48a,c,52] . Among them, Pd, Rh, Au and Ru showed high ECH activity for aldehyde model compounds upgrading [48a,52,53] . Pd exhibited excellent ECH activity for aromatic aldehydes [48a,c] .…”

“…Among them, Pd, Rh, Au and Ru showed high ECH activity for aldehyde model compounds upgrading [48a,52,53] . Pd exhibited excellent ECH activity for aromatic aldehydes [48a,c] . For instance, the ECH rate [μmol products g −1 catalyst h −1 ] of benzaldehyde with different metal cathodes followed the order of Pd/CF>Ru/CF>Rh/CF under the same other conditions (electrolyte: 47.5 wt% isopropanol, 47.5 wt% deionized water and 5.0 wt% acetic acid; potential: −1.1 V vs Ag/AgCl; ambient temperature and pressure) [48a] .…”

“…Pd exhibited excellent ECH activity for aromatic aldehydes [48a,c] . For instance, the ECH rate [μmol products g −1 catalyst h −1 ] of benzaldehyde with different metal cathodes followed the order of Pd/CF>Ru/CF>Rh/CF under the same other conditions (electrolyte: 47.5 wt% isopropanol, 47.5 wt% deionized water and 5.0 wt% acetic acid; potential: −1.1 V vs Ag/AgCl; ambient temperature and pressure) [48a] . Comparably, Pd/CF was the most active during ECH of benzaldehyde due to strong interactions between benzaldehyde and Pd/CF.…”