Enhanced Syngas Production from Dry Methane Reforming over a Ni Catalyst Supported on Calcium-Stabilized Zirconia

The increasing concentration of greenhouse gases, such as CH₄ and CO₂, in the environment is pushing the planet to the next level of global warming, where living creatures are becoming extinct one after another. The catalytic conversion of CH₄ and CO₂ together into syngas, known as dry reforming of methane (DRM), not only depletes the concentration of these gases but also provides an industrially important synthesis gas. Herein, the active sites (metallic Ni) supported over calcium-stabilized zirconia (Ni-xCaSZ; x = 8, 10, 12, 14 mol%) are investigated toward DRM reaction. Catalysts are characterized by X-ray diffraction, surface area and porosity, X-ray photoelectron spectroscopy, Raman spectroscopy, H₂-temperature-programmed reduction, and thermogravimetry. Calcium stabilizes the cubic phases of ZrO₂ and surges mixed oxide phases like cubic CaZrO₃ and monoclinic CaZr₄O₉. At high mol% of Ca, the interaction between CaO and ZrO₂ is grown, the covalence character about oxygen in MOM' bond is raised, the surface area of catalyst is increased, and coke deposition is restricted. Upon increasing mol% of Ca from 8 to 12 mol%, the moderate-level interaction of NiO over support is established, weak interaction of NiO is declined, and overall concentration of active sites is grown. As a result, 5Ni-12CaSZ achieves the highest 66% CH₄ conversion, 73% CO₂ conversion, and 0.86 H₂/CO ratio at 700 °C reaction temperature. An excess amount of calcium (14 mol%) changes the surface composition of CaZrO_x, as well as it may also block the oxide vacancy, which may inhibit the CO₂ activation vis-à-vis catalytic activity.