Cooperation of Ni and CaO at Interface for CO₂ Reforming of CH₄: A Combined Theoretical and Experimental Study

Abstract

Dry reforming of methane (DRM) is a promising chemical approach to convert greenhouse gases CO2 and CH4 into valuable fuels. Previous experimental study has shown that the addition of alkaline earth can promote the activity and stability of the Ni-based catalyst. However, the physical structure of alkaline earth additives on supports and their interaction with Ni particles should have significant influence for the catalytic performance of catalysts. To clarify the synthesis–structure–activity relationship for further improving these catalysts, the underlying reaction mechanism for DRM over size-confined Ni–CaO catalysts on neutral supports and the structure/effect of CaO as promoter were investigated combining density functional theory (DFT) calculation and experimental studies. The favored active sites for all elementary reactions were identified, and the activation energies of the reactions were calculated for the determination of the primary reaction pathways. DFT results found a cooperation effect between Ni and CaO, where the interface dissociates CO2, Ni activates CH4 dehydrogenation, and CaO attracts CO2. The interface between Ni and CaO was found to provide another channel to activate CO2 and decrease the energy barrier of CHO formation, contributing to the high efficiency and long-term stability of the catalyst. On the basis of the DFT results, the optimum stacking order between Ni and CaO was proposed, in good agreement with the experimental studies that synthesized and compared four catalysts with different Ni–CaO structures. The proposed Ni–CaO composite catalyst should be a promising catalyst for potential application in industrial dry reforming processes.

Investigation of new routes for the preparation of mesoporous calcium oxide supported nickel materials used as catalysts for the methane dry reforming reaction

“…We may also hypothesize, as Wu et al 45 did, that the efficient capture of CO 2 by the CaO supports, followed by its diffusion to the interface between CaO and the deposited Ni 0 nanoparticles, contributes to the good catalytic performances of the Ni x(OP) /CaO (TF) and Ni 10(TS) /CaO (HT) . Indeed, this could favor the oxidation of the intermediate activated carbon species arising from the CH 4 dissociation on the adjacent metallic nickel sites.…”

Dry Reforming of CH4/CO2by Stable Ni Nanocrystals on Porous Single‐Crystalline MgO Monoliths at Reduced Temperature

“…We further conduct the LEIS test of catalyst after durability test in Figure 5h S2, we summarize the typical operation of dry reforming of CH 4 /CO 2 at the temperature of 700-800 8 8Ca nd the feeding gas composition of 10-33 %CH 4 /10-33 %CO 2 /Ar and we show that the porous single-crystalline MgO monoliths with singlecrystalline Ni nanoparticles demonstrate much better conversion ratio as high as 95-100 %e ven in al ong-term operation of 500 hours at ar educed temperature of 700 8 8C. [32][33][34][35][36][37][38][39][40] We further conduct the dry reforming of 10 %CO 2 / 10 %CH 4 with the WHSV of 12-60 Lg cat À1 h À1 to validate the catalytic performance of porous single-crystalline MgO monoliths single-crystalline Ni nanoparticles.W eo bserve that the conversion rate of CO 2 /CH 4 increases from % 1.1 to % 1.5 Lg cat À1 h À1 with the WHSV ranging from 12 to 18 Lg cat À1 h À1 and generally maintain at ah igh level of % 1.1-1.4 Lg cat À1 h À1 even though the conversion ratio of 10 %CO 2 /10 %CH 4 shows al inear drop after the WHSV is as high as above 24 Lg cat À1 h À1 at 700 8 8C. This is because of that the limited surface area of the porous single-crystalline monoliths is not able to sufficiently accommodate the dry reforming reactions at surface.T he specific surface area is only % 21.2 m 2 g À1 for the porous single-crystalline MgO monoliths with single-crystalline Ni nanoparticles,w hich is only % 5-10 %o ft he specific surface area of many reported catalysts.A ctually,t he conversion rate of CO 2 /CH 4 per unit area of catalyst surface is pretty excellent and promising for the porous single-crystalline MgO monoliths.W es ummarize the conversion rate of CO 2 /CH 4 per unit surface area of catalysts at typical reaction conditions in Supplementary…”

Dry Reforming of CH4/CO2by Stable Ni Nanocrystals on Porous Single‐Crystalline MgO Monoliths at Reduced Temperature

“…Even with loaded Ni nanoparticles, they still demonstrate much lower CH 4 /CO 2 conversion and syngas yield. As shown in Table S2, we summarize the typical operation of dry reforming of CH 4 /CO 2 at the temperature of 700–800 °C and the feeding gas composition of 10–33 %CH 4 /10–33 %CO 2 /Ar and we show that the porous single‐crystalline MgO monoliths with single‐crystalline Ni nanoparticles demonstrate much better conversion ratio as high as 95–100 % even in a long‐term operation of 500 hours at a reduced temperature of 700 °C [32–40] …”