Tuning CO₂ Hydrogenation Selectivity by N-Doped Carbon Coating over Nickel Nanoparticles Supported on SiO₂

Abstract

Controlling the selectivity of CO2 hydrogenation is a challenge for the application of earth-abundant-based metal catalysts. Herein, we show that a high-temperature pyrolysis protocol can be applied to prepare a nickel catalyst embedded in N-doped carbon (Ni@NC), which provides an enhanced selectivity to CO in the nickel-catalyzed CO2 hydrogenation reaction under atmospheric pressure. The nitrogen-containing carbon overlayer was obtained through controlled pyrolysis of the nickel–1,10-phenanthroline complex impregnated on SiO2. The Ni@NC/SiO2 catalyst is more selective for CO, following the reverse water-gas shift reaction pathway, while an analogous “naked” Ni catalyst was more selective toward CH4, following the CO2/CO complete hydrogenation pathway. Although the Ni@NC/SiO2 catalyst has larger particle sizes than the naked Ni/SiO2 catalyst, the binding strength of CO to the Ni@NC surface is significantly weaker. Consequently, the CO intermediate easily desorbs instead of being converted into methane. Hence, selectivity toward CO, which is an important intermediate to methanol and C2+ products, or CH4 can be modulated by a simple modification of the Ni surface through controlled carbon deposition.

Particle Size Effects of Carbon Supported Nickel Nanoparticles for High Pressure CO2 Methanation

“…Wu et al . explained this particle size effect on CH 4 selectivity by a lower H 2 surface coverage of (sub‐)nm particles compared to 9 nm particles at atmospheric pressure, [15] although this was questioned by Arpini et al [58] . From our reaction order study it is clear that the surface coverage of H 2 is not a relevant factor under our conditions (Table S6), as described before.…”

“…They tested their catalysts at a CO 2 conversion < 3 % and still observed significant CO formation, [35] which is in line with our results at low conversions. Wu et al explained this particle size effect on CH 4 selectivity by a lower H 2 surface coverage of (sub-)nm particles compared to 9 nm particles at atmospheric pressure, [15] although this was questioned by Arpini et al [58] From our reaction order study it is clear that the surface coverage of H 2 is not a relevant factor under our conditions (Table S6), as described before. Thus we were able to confirm that the selectivity trends are not related to the presence or absence of dissociated hydrogen on the Ni surface.…”

“…Thus we were able to confirm that the selectivity trends are not related to the presence or absence of dissociated hydrogen on the Ni surface. The binding strength of CO could also be a factor to push the selectivity to CH 4 or CO. [59] Carbon coated Ni particles [58] or the formation of Ni 3 C [59] species can affect the binding strength of CO and thus influence the selectivity. However, a Ni 3 C phase was not observed in XRD before or after catalysis.…”

Addressing the CO2 challenge through thermocatalytic hydrogenation to carbon monoxide, methanol and methane

“…While the bulk NiO is appropriate for CO 2 methanation, the highly dispersed counterpart is effective in the RWGS reaction. 112 Other oxide materials such as SBA-15, 118 MgO, 111 Al 2 O 3 , 114 SiO 2 , 113,116 and In 2 O 3 115 have been used as support for nickel.…”

Design de nanocatalisadores híbridos de níquel e carbono e suas aplicações em reações de hidrogenação

“…[16] Para isso, uma vasta gama de metais de transição vem sendo estudada, como Ru, [20] Rh, [21] Pt, [22] Pd, [23] Re, [24] Co, [25] Fe, [26] e Ni. [27][28][29][30] Catalisadores de Ni suportados têm sido extensivamente investigados e são particularmente eficientes na conversão de CO2 via reação de hidrogenação com H2(g), [31][32][33] (com sucesso parcial) H2 a partir de vapor d'água e CO utilizando um catalisador de óxido de ferro, durante o estudo da reação de deslocamento gás-água. [36] A RWGS trata-se de uma reação endotérmica, portanto favorecida por altas temperaturas, porém reversível.…”