Crystal Plane Engineering to Boost the Coke Resistance of a Ni/NaY Catalyst for Dry Reforming of Methane

Abstract

Catalyst deactivation caused by carbon deposition remains a major obstacle to the large-scale application of dry reforming of methane (DRM). Previous studies have primarily focused on controlling particle size and electronic properties of the metal component to improve coke resistance, while the role of the metal crystal plane has always been overlooked. Herein, metallic Ni with various proportions of Ni(111) and Ni(220) crystal planes was fabricated on the Ni/NaY catalyst by modulating nickel precursors. The reduction of NiO tends to form Ni(111), whereas the reduction of nickel silicate generated during the in situ solid grinding synthesis favors the formation of Ni(220). Therefore, the in situ-synthesized Ni/NaY catalyst exhibits a higher Ni(220) content than the impregnation-prepared counterpart. The rate-limiting step for CH4 activation shifts from CH4→ CH3* on Ni(111) to CH3*→ CH2* on Ni(220), preserving more saturated CHx* active intermediates and suppressing excessive CH4 cracking. Besides, the CO2 activation on Ni(220) primarily follows the pathway of CO2→ HCOO*, which is distinct from that of CO2→ HCO3*→ HCOO* on Ni(111). This direct conversion of CO2 increases the concentration of OH* generated from HCOO* decomposition. The resulting OH* promotes oxidization of the CHx* into CO, thereby inhibiting excessive CH4 cracking and carbon deposition. Therefore, an efficient dynamic equilibrium between CH4 activation and the timely oxidation of CHx* intermediates is achieved by engineering the Ni crystal plane, enhancing both activity and coke resistance. The Ni(220)-enriched catalyst exhibits negligible carbon deposition compared with the Ni(111)-enriched counterpart after 12 h of reaction while maintaining CH4 and CO2 conversions of 83.7% and 86.5%, respectively. This work provides a strategy to boost coke resistance of Ni-based DRM catalysts through crystal plane engineering.