Ethanol steam reforming on nanostructured catalysts of Ni, Co and CeO 2 : Influence of synthesis method on activity, deactivation and regenerability

IR Studies of Ethoxy Groups on CeO2

The reaction of ethanol with a surface of CeO₂ was studied using IR spectroscopy. In some experiments, CeO₂ was pretreated in a vacuum at 820 K which caused a partial reduction. In other experiments, CeO₂ was reduced with hydrogen at 770 K. We also used CeO₂ oxidized by oxygen treatment at 670 K. At low coverages, ethoxy groups and new surface OH groups were formed and water was not produced. On the other hand, at higher loading surfaces, Ce-OH was consumed and ethoxy groups and water were formed. Three kinds of ethoxyls were found on CeO₂: monodentate, bidentate, and tridentate ones. They were characterized by various frequencies of symmetrical, asymmetrical, and combinational bands of C-C-O units. The reduction of CeO₂ increased the contribution of tridentate ethoxyls and the oxidation increased the contribution of monodentate ones. At higher temperatures, ethoxy groups were oxidized to acetate ions with the formation of new surface OH groups. Monodentate ethoxyls were the most reactive and tridentate ones were the least reactive during oxidation. The amounts of acetate species were the highest for the oxidized CeO₂.

Steam Reforming of Bioethanol Using Metallic Catalysts on Zeolitic Supports: An Overview

Hydrogen is considered one of the energy carriers of the future due to its high mass-based calorific value. Hydrogen combustion generates only water, and it can be used directly as a fuel for electricity/heat generation. Nowadays, about 95% of the hydrogen is produced via conversion of fossil fuels. One of the future challenges is to find processes based on a renewable source to produce hydrogen in a sustainable way. Bioethanol is a promising candidate, since it can be obtained from the fermentation of biomasses, and easily converted into hydrogen via steam catalytic reforming. The correct design of catalysts and catalytic supports plays a crucial role in the optimization of this reaction. The best results have to date been achieved by noble metals, but their high costs make them unsuitable for industrial application. Very satisfactory results have also been achieved by using nickel and cobalt as active metals. Furthermore, it has been found that the support physical and chemical properties strongly affect the catalytic performance. In this review, zeolitic materials used for the ethanol steam reforming reaction are overviewed. We discuss thermodynamics, reaction mechanisms and the role of active metal, as well as the main noble and non-noble active compounds involved in ethanol steam reforming reaction. Finally, an overview of the zeolitic supports reported in the literature that can be profitably used to produce hydrogen through ethanol steam reforming is presented.

Thermocatalytic Hydrogen Production Through Decomposition of Methane-A Review

Consumption of fossil fuels, especially in transport and energy-dependent sectors, has led to large greenhouse gas production. Hydrogen is an exciting energy source that can serve our energy purposes and decrease toxic waste production. Decomposition of methane yields hydrogen devoid of COx components, thereby aiding as an eco-friendly approach towards large-scale hydrogen production. This review article is focused on hydrogen production through thermocatalytic methane decomposition (TMD) for hydrogen production. The thermodynamics of this approach has been highlighted. Various methods of hydrogen production from fossil fuels and renewable resources were discussed. Methods including steam methane reforming, partial oxidation of methane, auto thermal reforming, direct biomass gasification, thermal water splitting, methane pyrolysis, aqueous reforming, and coal gasification have been reported in this article. A detailed overview of the different types of catalysts available, the reasons behind their deactivation, and their possible regeneration methods were discussed. Finally, we presented the challenges and future perspectives for hydrogen production via TMD. This review concluded that among all catalysts, nickel, ruthenium and platinum-based catalysts show the highest activity and catalytic efficiency and gave carbon-free hydrogen products during the TMD process. However, their rapid deactivation at high temperatures still needs the attention of the scientific community.

Copper Tricomponent Catalysts Application for Hydrogen Production from Ethanol

The application of copper-based catalysts in the production of pure hydrogen in the steam reforming of ethanol was performed. The tricomponent Cu/Zr catalysts with about 4 mass% addition of nickel, cobalt, or cerium have been prepared in our laboratory. The properties of obtained catalysts were compared with bimetallic Cu/Zr catalyst prepared and tested according to the same procedure. Catalytic tests were carried out in the continuous flow fixed–bed reactor in the wide temperature range of 433–593 K for initial molar ratio of ethanol to water equal to 1:3. Catalysts were characterized by XRD, TPR, CO2–TPD, and TPO methods. Cu/Zr/Ce catalyst proved to be the best; hydrogen yield reached the value of 400 L/(kgcat.∙h), selectivity towards carbon monoxide was below 0.5% and the one towards methane wasnot detected. Additions of Ni or Co did not bring significant improvement in activity.

Microemulsion vs. Precipitation: Which Is the Best Synthesis of Nickel–Ceria Catalysts for Ethanol Steam Reforming?

Ethanol steam reforming is one of the most promising ways to produce hydrogen from biomass, and the goal of this research is to investigate robust, selective and active catalysts for this reaction. In particular, this work is focused on the effect of the different ceria support preparation methods on the Ni active phase stabilization. Two synthetic approaches were evaluated: precipitation (with urea) and microemulsion. The effects of lanthanum doping were investigated too. All catalysts were characterized using N2-physisorption, temperature programmed reduction (TPR), XRD and SEM, to understand the influence of the synthetic approach on the morphological and structural features and their relationship with catalytic properties. Two synthesis methods gave strongly different features. Catalysts prepared by precipitation showed higher reducibility (which involves higher oxygen mobility) and a more homogeneous Ni particle size distribution. Catalytic tests (at 500 °C for 5 h using severe Gas Hourly Space Velocity conditions) revealed also different behaviors. Though the initial conversion (near complete) and H2 yield (60%, i.e., 3.6 mol H2/mol ethanol) were the same, the catalyst prepared by microemulsion was deactivated much faster. Similar trends were found for La-promoted supports. Catalyst deactivation was mainly related to coke deposition as was shown by SEM of the used samples. Higher reducibility of the catalysts prepared by the precipitation method led to a decrease in coke deposition rate by facilitating the removal of coke precursors, which made them the more stable catalysts of the reaction.

Sustainable Production of Hydrogen by Steam Reforming of Ethanol Using Cobalt Supported on Nanoporous Zeolitic Material

Cobalt catalysts supported on Y zeolite and mesoporized Y zeolite (Y-mod) have been studied in steam reforming of ethanol (SRE). Specifically, the effect of the mesoporosity and the acidity of the y zeolite as a support has been explored. Mesoporous were generated on Y zeolite by treatment with NH4F and the acidity was neutralized by Na incorporation. Four cobalt catalysts supported on Y zeolite have been prepared, two using Y zeolite without mesoporous (Co/Y, Co/Y-Na), and two using Y zeolite with mesoporous (Co/Y-mod and Co/Y-mod-Na). All catalysts showed a high activity, with ethanol conversion values close to 100%. The main differences were found in the distribution of the reaction products. Co/Y and Co/Y-mod catalysts showed high selectivity to ethylene and low hydrogen production, which was explained by their high acidity. On the contrary, neutralization of the acid sites could explain the higher hydrogen selectivity and the lower ethylene yields exhibited by the Co/Y-Na and Co/Y-mod-Na. In addition, the physicochemical characterization of these catalysts by XRD, BET surface area, temperature-programmed reduction (TPR), and TEM allowed to connect the presence of mesoporous with the formation of metallic cobalt particles with small size, high dispersion, and with high interaction with the zeolitic support, explaining the high reforming activity exhibited by the co/y-mod-Na sample as well as its higher hydrogen selectivity. It has been also observed that the formation of coke is affected by the presence of mesoporous and acidity. Both properties seem to have an opposite effect on the reforming catalyst, decreasing and increasing the coke deposition, respectively.

Investigation on binary copper-based catalysts used in the ethanol steam reforming process

The use of copper-based binary catalysts, Cu/Zr oxides and Cu/Al oxides, has been examined to produce hydrogen from ethanol in the ethanol steam reforming process. The examined catalysts were compared with non-noble bicomponent catalysts consisting of oxides of nickel and cobalt: Ni/Zr Co/Zr, Ni/Al and Co/Al, prepared and tested in the identical way. Catalytic tests were carried out in the fixed-bed reactor in the temperature range 433–873 K for initial molar ratio of ethanol to water equal to 1:3. Ethanol conversion approached near 100%. Catalysts were characterized by XRD, TPR. Cu/Zr oxides. The catalyst showed very good selectivity. It is significant that carbon monoxide appeared only above 600 K and its selectivity has not exceeded 3% in the higher temperature range. No methane has been detected. Hydrogen yield was relatively stable in the temperature range from 513 to 873 K. Similarly, in the presence of Cu/Al oxides neither CO nor CH4 were found in the products. The correlation between activity of examined catalysts and textural properties was not found.

Sustainable hydrogen-rich syngas from steam reforming of bio-based acetic acid over ZnO and CeO2–ZnO supported Ni-based catalysts

Sustainable hydrogen-rich syngas from steam reforming (SR) of bio-based acetic acid over ZnO and CeO₂–ZnO supported Ni-based catalysts was studied by means of a bench-scale fixed-bed unit combined with NDIR/TCD techniques. The effects of Ni/ZnO catalysts with different nickel loadings (5–15%), temperature (T = 500–900 °C), steam to carbon molar ratio (S/C = 1–5) and weight hourly space velocity (WHSV = 3–7 h⁻¹) on SR of acetic acid were explored. In addition, the influence of CeO₂ addition on the catalytic performance was assessed to investigate the improvement effect of Ce as a promoter on the catalytic activity. As the nickel loading increased from 5 to 15%, the H₂ yield increased significantly from 31.0 to 51.0% with a growth rate of 64.5%, while the CO yield first decreased from 31.6 to 27.7% and then increased to 35.7%. Between 500 and 900 °C, the yields of H₂ and CO first increased and then decreased, corresponding to the peak yields of 51.0% and 35.7% at 800 °C, respectively. S/C gave a similar trend of H₂ yield to the T, while the CO yield continued to decrease with increasing S/C from 1 to 5. The H₂ yield gradually decreased from 54.1 to 28.7% as the WHSV increased, while the peak value of CO yield was 35.7%, corresponding to WHSV = 5. The addition of 25 wt% CeO₂ to the Ni/ZnO catalyst with a nickel loading of 15% improved the H₂ yield from 51.0 to 74.0% when reforming acetic acid under the optimal operating conditions of T = 800 °C, S/C = 3 and WHSV = 5 h⁻¹. The CO yield was reduced from 35.7 to 33.2%, and the corresponding H₂/CO ratio increased from 2.9 to 4.5. The excellent catalyst stability was obtained in the SR of acetic acid using Ni/CeO₂–ZnO catalyst. H₂ yield was reduced from 76.0 to 73.5% with a decrease of 3.4%, while CO yield increased from 32.1 to 41.3% with a growth rate of 28.7% within 15–360 minutes.

Variation of hydrogen-rich syngas from steam reforming of bio-based acetic acid over Ni/ZnO and Ni/CeO₂–ZnO catalysts was assessed.