Abstract
The ethanol steam reforming process (ESR) over cobalt-based zeolitic catalysts, differing significantly in the structure, was comprehensively examined. The cobalt spinel phase (10wt%) was deposited on the surface of USY and ZSM-5 zeolites (Si/Al ratio of 31). The catalysts were characterized in terms of their chemical (ICP) and phase composition (XRD), textural properties (low-temperature N2 adsorption), morphology (STEM/EDX), and reducibility (H2-TPR). The aforementioned characteristics were supplemented by the catalysts’ acidity and redox properties investigations (quantitative FT-IR studies of pyridine and carbon monoxide adsorption). Catalysts' activity was evaluated in the ESR process at 500C for various ethanol/water mixtures. Both catalysts exhibited 100% ethanol conversion, whereas their selectivity towards H2, CO2, and C2H4 strongly depended on the applied ethanol to water molar ratio. Comparable selectivities observed for the 1:4 ratio were improved for the 1:9 ratio for both catalysts, as expected. For the ratio of 1:12, the significant difference in the reaction paths (the ethanol dehydration for CoUSY and the ethanol steam reforming for CoZSM-5) was explained by the cobalt reoxidation process facilitated by water molecules for the CoUSY. The superior overall performance of the CoZSM-5 catalyst in the ESR process, in comparison to CoUSY, also results from its almost three times enhanced accessibility of the cobalt species, as confirmed by the quantitative FT-IR studies of CO sorption. The microscopic studies also indicated a better dispersion of the cobalt phase supported on the ZSM-5 support. Thus, the structure of ZSM-5 zeolite assures higher cobalt active phase dispersion being more beneficial for the ESR process.
Highlights
Hydrogen-derived energy sources are a sustainable and environmentally friendly alternative to the utilization of fossil fuels, for which the availability of reserves is subject to high uncertainty
The co-modified zeolitic catalysts (CoUSY and CoZSM-5) were thoroughly characterized by means of XRD, TEM/EDX, TPR, and FT-IR sorption studies to define the effect of the comoieties dispersion and metal-support interactions on their catalytic performance in the ethanol steam reforming (ESR) process carried out at variable water content
From the X-ray diffractograms collected in Figure 1, it can be inferred that there was almost no change in the crystal structure of USY zeolite or ZSM-5 zeolite after the cobalt addition
Summary
Hydrogen-derived energy sources are a sustainable and environmentally friendly alternative to the utilization of fossil fuels, for which the availability of reserves is subject to high uncertainty. The rapid reaction between the acetate species and water to form COx and H2, without the involvement of the CH4 formation, is responsible for the high performance of the Co-based catalysts in the ESR process (Sekine et al, 2014; Ogo et al, 2015; Ogo and Sekine, 2020). The co-modified zeolitic catalysts (CoUSY and CoZSM-5) were thoroughly characterized by means of XRD, TEM/EDX, TPR, and FT-IR sorption studies to define the effect of the comoieties dispersion and metal-support interactions on their catalytic performance in the ESR process carried out at variable water content. The activity and selectivity of cobalt-containing zeolite catalysts in the ESR reaction were determined in a continuous fixed-bed quartz reactor (Microactivity Reference unit, PID Eng & Tech.) at 500°C. Where Cout is the molar concentration of the hydrogen-containing products in the postreaction mixture (mol%)
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