Coupling of Methane to Ethane, Ethylene, and Aromatics over Nickel on Ceria–Zirconia at Low Temperatures

Abstract

Methane is converted over nickel on ceria zirconia (Ni/CZ) into ethane, aromatics, and hydrogen at steady state up to the thermodynamic limit at temperatures of 350 to 500 °C. At 450 and 500 °C, traces of ethylene are also produced. Ni/NiO particles activate methane and couple the resulting surface species to hydrocarbon products. Large Ni particles are responsible for the formation of carbonaceous deposits. Furthermore, aromatics are formed on these sites. Smaller Ni/NiO particles are responsible for the formation of ethane and ethylene and appear to provide sustained activity. It is suggested that these Ni sites are too small to assemble aromatic deposits, and hence they remain active throughout the reaction.

Selective Oxidation of Methane to Methanol over Ceria‐Zirconia Supported Mono and Bimetallic Transition Metal Oxide Catalysts

“…The presence of supported metal oxide cluster resulted in additional reduction peaks. Specifically, the first peaks in the H 2 ‐TPR profiles for the catalyst samples, such as the peak at 164 °C for the NiO/CZ, and the peak at 110 °C for the CuO/CZ, were assigned to the consumption of the adsorbed oxygen species on the support [24b,c,31] . The concentration of the adsorbed surface oxygen was less in samples with Fe than the others.…”

“…During the in‐situ IR spectroscopy experiments, the only source of oxygen was that stored within the catalysts. Our previous study revealed that the NiO clusters remained oxidized upon exposure to methane at 450 °C while there was active oxygen in the CZ support indicating that the latter oxygen species play the key role in oxidation reactions [24b] . Therefore, the formation of methoxy groups is probably related to the reducibility of the CZ support.…”

“…The redox active sites on CZ supports induce a strong metal support interaction (SMSI), which can stabilize well‐dispersed metal oxide clusters or metal cations [24b,44] . These well‐dispersed clusters generate interfacial defect sites, which in turn enhance the reducibility of the CZ support [24b,31d] . Such catalysts often demonstrate superior catalytic activities.…”

“…A methane pre‐treatment step at 450 °C was performed to remove highly active adsorbed surface oxygen species that promote the formation of CO 2 [24c] . Using a weak reducing agent, methane, avoids the over‐reduction of NiO to Ni, as indicated by the in‐situ XAS experiment performed in our previous study [24b] . The CO 2 yield decreased with time on stream by more than 85 % over all catalysts, while the yield towards methanol increased (Figure 4), indicating that the conversion of methane to CO 2 and methanol was achieved over different active sites or involved different active oxygen species from the CZ support.…”

“…The CO 2 yield decreased with time on stream by more than 85 % over all catalysts, while the yield towards methanol increased (Figure 4), indicating that the conversion of methane to CO 2 and methanol was achieved over different active sites or involved different active oxygen species from the CZ support. Considering the fact that at least 90 % of the coke were formed during first 100 min on stream (Table S3 and S4), it is likely that coke formation covered certain larger metal oxide clusters [24b] . However, it is also possible that a change in the speciation of active oxygen species could affect the performance of the catalyst [55] .…”