Enhanced Catalytic Hydrodeoxygenation of Activated Carbon-Supported Metal Catalysts via Rapid Plasma Surface Functionalization

Abstract

We employ a nonthermal, He/O2 atmospheric plasma as an efficient surface functionalization method of activated carbons. We show that plasma treatment rapidly increases the surface oxygen content from 4.1 to 23.4% on a polymer-based spherical activated carbon in 10 min. Plasma treatment is 3 orders of magnitude faster than acidic oxidation and introduces a diverse range of carbonyl (CO) and carboxyl (O–CO) functionalities that were not found with acidic oxidation. The increased oxygen functionalities reduce the particle size of a high 20 wt % loading Cu catalyst by >44% and suppress the formation of large agglomerates. Increased metal dispersion exposes additional active sites and improves the yield of hydrodeoxygenation of 5-hydroxymethyl furfural to 2,5-dimethyl furan, an essential compound for biofuel replacement, by 47%. Surface functionalization via plasma can advance catalysis synthesis while being rapid and sustainable.

Plasma-Enabled Ligand Removal for Improved Catalysis: Furfural Conversion on Pd/SiO2

“…A signal corresponding to the C–O species at 286.1 eV appears and that for C–N at 286.5 eV disappears after the 3–9 h plasma treatment. The He/O 2 plasma can degrade and oxidize the PVP to carbon oxides that adsorb on the sample surface and might not easily desorb due to the low plasma operating temperature (less than 100 °C). ,, This result aligns with FTIR findings of no C–H stretching bands seen after 3 h of plasma treatment. Hence, the CO and C–O signals of the 3, 6, and 9 h plasma-treated samples were assigned to oxidized carbon species formed during plasma exposure.…”

“…Both shape and size remain unchanged after 9 h of plasma treatment (Figure d–f and Figure S4d–f), indicating that sintering is avoided due to the low-temperature of the Dielectric Barrier Discharge (DBD) plasma. In another study by our group, we found that the neutral gas temperature is lower than 100 °C, and thus, the thermal effect is expected to be minimal . In contrast, the Pd nanocubes, upon 2 h of calcination at 300 °C, became polycrystalline with an average particle size of 12.4 nm (Figure g–i and Figure S4g–i).…”

“…In another study by our group, we found that the neutral gas temperature is lower than 100 °C, and thus, the thermal effect is expected to be minimal. 18 In contrast, the Pd nanocubes, upon 2 h of calcination at 300 °C, became polycrystalline with an average particle size of 12.4 nm (Figure 2g−i and Figure S4g−i). The low-temperature calcination removes ligands from noble metal nanoparticles by partly converting them to coke, 32,33 but also alters their shape and size.…”

“…NTP has been used to functionalize catalysts and supports to improve surface properties 15 (i.e., hydrophobic surfaces), enhance Brønsted and Lewis acidity, 16,17 and increase metal dispersion. 18 NTP can replace conventional calcination, avoiding thermal effects, 19,20 and remove templates from SBA-15 21 and ZSM-5 22 ligands in nanoparticle synthesis is less investigated and has only been studied under vacuum. 23−25 Ligand removal from Au and Ag nanoparticles by NTPs 26−29 led to a slight increase in particle size and increased activity in oxygen reduction reaction (ORR), 27 epoxidation of propylene, 28,29 and hydrogenation of acetylene.…”

“…Nonthermal plasma (NTP) has a low energy demand, minimal environmental footprint, and abundant reactive species. NTP has been used to functionalize catalysts and supports to improve surface properties (i.e., hydrophobic surfaces), enhance Brønsted and Lewis acidity, , and increase metal dispersion . NTP can replace conventional calcination, avoiding thermal effects, , and remove templates from SBA-15 and ZSM-5 zeolites.…”