In this paper, we show how the composition of bimetallic Fe−Ni exsolution can be controlled by the nature and concentration of oxygen vacancies in the parental matrix and how this is used to modify the performance of CO 2 -assisted ethane conversion. Mesoporous A-sitedeficient La 0.4 Sr 0.6−α Ti 0.6 Fe 0.35 Ni 0.05 O 3±δ (0 ≤ α ≤ 0.2) perovskites with substantial specific surface area (>40 m 2 /g) enabled fast exsolution kinetics (T < 500 °C, t < 1 h) of bimetallic Fe−Ni nanoparticles of increasing size (3−10 nm). Through the application of a multitechnique approach we found that the A-site deficiency determined the concentration of oxygen vacancies associated with iron, which controlled the Fe reduction. Instead of homogeneous bimetallic nanoparticles, the increasing Fe fraction from 37 to 57% led to the emergence of bimodal Fe/Ni 3 Fe systems. Catalytic tests showed superior stability of our catalysts with respect to commercial Ni/Al 2 O 3 . Ethane reforming was found to be the favored pathway, but an increase in selectivity toward ethane dehydrogenation occurred for the systems with a low metallic Fe fraction. The chance to control the reduction and growth processes of bimetallic exsolution offers interesting prospects for the design of advanced catalysts based on bimodal nanoparticle heterostructures.
CO2 hydrogenation toward methane, a reaction of high environmental and sustainable energy importance, was investigated at 200–600 °C and H2/CO2 = 4/1, over Rh nanoparticles dispersed on supports with different oxygen storage capacity characteristics (γ-Al2O3, alumina-ceria-zirconia, and ceria-zirconia). The effects of the support OSC and Rh particle size on reaction behavior under both integral and differential conditions were investigated, to elucidate the combined role of these crucial catalyst design parameters on methanation efficiency. A volcano-type variation of methanation turnover frequency was found in respect to support OSC; Rh/ACZ, with intermediate OSC, was the optimal catalyst. The structure sensitivity of the reaction was found to be a combined function of support OSC and Rh particle size: For Rh/γ-Al2O3 (lack of OSC) methanation was strongly favored on small particles—the opposite for Rh/CZ (high OSC). The findings are promising for rational design and optimization of CO2 methanation catalysts by tailoring the aforementioned characteristics.
The time-on-stream catalytic performance and stability of 8 wt. % Ni catalyst supported on two commercially available catalytic supports, ZrO 2 and 15 wt.% WO 3 -ZrO 2 , was investigated under the biogas dry reforming reaction for syngas production, at 750 • C and a biogas quality equal to CH 4 /CO 2 = 1.5, that represents a common concentration of real biogas. A number of analytical techniques such as N 2 adsorption/desorption (BET method), XRD, H 2 -TPR, NH 3 -and CO 2 -TPD, SEM, ICP, thermal analysis (TGA/DTG) and Raman spectroscopy were used in order to determine textural, structural and other physicochemical properties of the catalytic materials, and the type of carbon deposited on the catalytic surface of spent samples. These techniques were used in an attempt to understand better the effects of WO 3 -induced modifications on the catalyst morphology, physicochemical properties and catalytic performance. Although Ni dispersion and reducibility characteristics were found superior on the modified Ni/WZr sample than that on Ni/Zr, its dry reforming of methane (DRM) performance was inferior; a result attributed to the enhanced acidity and complete loss of the basicity recorded on this catalyst, an effect that competes and finally overshadows the benefits of the other superior properties. Raman studies revealed that the degree of graphitization decreases with the insertion of WO 3 in the crystalline structure of the ZrO 2 support, as the I D /I G peak intensity ratio is 1.03 for the Ni/Zr and 1.29 for the Ni/WZr catalyst.
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