CoFe, CoW, NiFe and NiW bimetallic pairs deposited over the CeO2-ZrO2 promoted ordered mesoporous g-Al2O3, were tested in methane dry reforming reaction. The CoFe/AlCZ and NiFe/AlCZ catalysts achieved high and stable methane conversion rates of 8.8 and 6.0 mmol CH4/(gcat min), respectively. Activity of tungsten containing catalysts (CoW/AlCZ and NiW/AlCZ) was substantially lower, compared to iron containing catalysts (2.8 and 0.8 mmol CH4/(gcat min), respectively) and their deactivation was likely related to sintering and oxidation of active metal clusters. Low carbon content was accumulated on the surface of spent NiFe/AlCZ, CoFe/AlCZ and NiW/AlCZ catalysts after 20 h tests (0.6-1.2 wt. %), indicating high efficiency of the redox promoter under dry reforming conditions.
COBISS.SI-ID: 5837594
This study explores CeZrO2 deposited over commercial β-SiC, and a highly ordered 3D β-SiC synthesised in the laboratory via electrophoretic deposition, as well as γ-Al2O3 in order to prepare three types of dual support for NiCo bimetallic catalyst in CH4–CO2 dry reforming (DR). CeZrO2 was deposited over γ-Al2O3 and β-SiC by dry impregnation (DI), wet impregnation (WI) and 2-step deposition precipitation (DP). XRD analysis indicated that the constituents of the dual supports were retained after calcination, as well as before and after the DR reaction. CeZrO2 remained as a mixed oxide solid solution, whilst alumina formed spinel structures with Ni and Co before the catalysts were reduced in H2 during the pretreatment step prior to the activity tests. During 550 h stability tests, WI, 2-step SICAT/CeZrO2 and 2-step γ-Al2O3/CeZrO2 solids were identified as the most promising catalysts, maintaining high DR activities without deactivation. Notably, 2-step SiC(SICAT) and 2-step γ-Al2O3/CeZrO2 samples recorded the highest yield (H2 = 77%, CO = 90%; H2 = 71%, CO = 81%), with a coke content of 7.7 and 0.6 wt.%, respectively. Carbon deposition for the former is high; contrarily, for WI SiC(SICAT) solid, it accumulated a lower amount of 2.6 wt.%. No agglomeration of CeZrO2 and NiCo phases was observed, evidencing excellent robustness and thermal resistance of these dual supports.
COBISS.SI-ID: 37574917
This study investigates how morphology, active metal content and oxygen storage capacity of various bimetallic NiCo/CeZrO2 materials influence their catalytic activity and stability in the methane dry reforming reaction. Catalyst preparation procedure and chemical composition were steered to finally obtain materials, which do not accumulate carbon during the CH4/CO2 reforming reaction. Oxygen storage capacity of the CeZrO2 catalyst support was identified to play a vital role in retarding carbon accumulation over the tested NiCo/CeZrO2 materials. This property can be fully developed when a nanocrystalline solid solution of CeO2 and ZrO2 is formed. Secondly, a high dispersion of nickel and cobalt is crucial for two reasons: (i) catalysts which contain larger NiCo bimetallic particles (for example with 12-18 wt. % active metal loading) exhibit a low metal-support interphase that results in enhanced coke formation rates; (ii) additionally, only a marginal gain in methane reforming rates are achieved at higher loadings, compared to catalysts with a 3-6 wt. % active metal content.
COBISS.SI-ID: 37867525
Stable catalytic performance is one of the most important aspects of heterogeneous catalysis. Synthesized supported transition metal catalysts were thoroughly characterized using advanced surface-sensitive and bulk in-situ and operando techniques. Changes in physical and chemical properties of tested materials were correlated to the observed oscilation in their catalytic activity. It was discovered that oxidation of NiCo bimetallic clusters is strongly size-dependant and is the primary reason for the observed catalyst deactivation. Catalyst regeneration was connected partly to transition of growing (in)active oxide clusters back to their initial metallic state and recrystallization of the Ceria-zirconia redox support. In depth materials characterization is crucial and will be employed also when analyzing the performance of newly developed catalysts in this research project.
COBISS.SI-ID: 37294341