Hierarchical Layered Porous SiO2 Supported Bimetallic NiM/EXVTM-SiO2 (M = Co, Cu, Fe) Catalysts Derived from Vermiculite for CO2 Reforming of Methane

Supercritical fluid-assisted modification combined with the resynthesis of SmCoO3 as an effective tool to enhance the long-term performance of SmCoO3-derived catalysts for the dry reforming of methane to syngas

The dry reforming of methane to syngas (DRM) is of increasing significance concerning, first, the production of raw materials for commercial organic/petrochemical syntheses and for hydrogen energetic, and, second, the utilization of two most harmful greenhouse gases. Herein, new SmCoO₃-based DRM catalysts derived from heterometallic precursors and operated without preliminary reduction are reported. For the first time, the effect of supercritical fluids-assisted modification of the SmCoO₃-derived catalysts combined with the re-oxidation of spent catalysts to SmCoO₃ onto its long-term performance was studied. In particular, the modification of heterometallic precursors by supercritical antisolvent precipitation (SAS) considerably decreases coke formation upon the exploitation of the derived SmCoO₃ sample. Moreover, the re-oxidation of the corresponding spent catalysts followed by pre-heating under N₂ affords catalysts that stably provide syngas yields of 88-95% for at least 41 h at 900 °C. The achieved yields are among the highest ones currently reported for DRM catalysts derived from both LnMO₃ perovskites and related oxides. The origins of such good performance are discussed. Given the simplicity and availability of all the applied methods and chemicals, this result opens prospects for exploiting SAS in the design of efficient DRM catalysts.

The Effect of Different Promoters (La2O3, CeO2, and ZrO2) on the Catalytic Activity of the Modified Vermiculite-Based Bimetallic NiCu/EXVTM-SiO2 Catalyst in Methane Dry Reforming

An X-NiCu/EXVTM-SiO₂ (X = La, Ce, and Zr) catalyst was successfully prepared by using modified vermiculite as a support by the impregnation method. This experiment investigated the effects of La₂O₃, CeO₂, and ZrO₂ promoters on the activity of the NiCu/EXVTM-SiO₂ catalyst. The study found that the addition of three different metal oxides did not improve the activity of the NiCu/EXVTM-SiO₂ catalyst. On the contrary, some Ni active sites were covered by the promoter, which reduced the number of active sites, resulting in its catalytic activity lower than NiCu/EXVTM-SiO₂. In addition, the promoted catalysts that were repeatedly calcined two times can significantly reduce the textural property as well as active sites of the catalyst, resulting in the lower activity. However, in X-NiCu/EXVTM-SiO₂, Ce-NiCu/EXVTM-SiO₂ showed relatively high initial catalytic activity, with the initial conversion rate of CH₄ reaching 60.1% and the initial conversion rate of CO₂ reaching 89.1%. This is mainly because the catalyst has a stronger basic site on the surface to facilitate the adsorption of CO₂ molecules, and the smaller metal particle size is also conducive to the cleavage of C-H bonds.

CeO2- and CaO-Promoted Precipitation Method for One-Step Preparation of Vermiculite-Based Multilayer Mesoporous Ni-Based Catalysts for Dry Reforming of Methane

In this paper, a molecular sieve (VSiO2) prepared from modified vermiculite is used as a support, and a multilayer mesoporous catalyst, Ni-VSiO2, is prepared while the active components are loaded in one step by the precipitation method. The catalyst is further modified by adding additives Ca and Ce to prepare the catalyst Ni-5x-VSiO2 (x = Ce, Ca) and is used for the dry reforming of methane reaction. The catalyst is characterized by X-ray fluorescence, Brunauer-Emmett-Teller analysis, scanning electron microscopy, hydrogen temperature-programmed reduction test, transmission electron microscopy, thermogravimetric analysis, and other technical means. The result shows that under a normal pressure of 750 °C, the catalyst Ni-Ca-VSiO2 has good stability. The catalyst Ni-Ce-VSiO2 has good activity, stability and carbon deposition resistance, and the conversion rates of CO2 and CH4 are 88% and 78%, respectively. This is because the mesoporous structure allows Ni nanoparticles to enter the pores of the catalyst support, thereby inhibiting the aggregation of the active component Ni and improving its sintering resistance. CeO2 additives provide more oxygen vacancies to inhibit the formation of carbon deposits. At the same time, the strong interaction between the active component Ni and the additive CeO2 is also beneficial to improve its sintering resistance.