Elucidation of metal and support effects during ethanol steam reforming over Ni and Rh based catalysts supported on (CeO2)-ZrO2-La2O3

Global Vision of the Reaction and Deactivation Routes in the Ethanol Steam Reforming on a Catalyst Derived from a Ni-Al Spinel

Ethanol steam reforming (ESR) over a Ni/Al2O3 catalyst prepared by reduction of a NiAl2O4 spinel is a promising alternative route to produce H2 from biomass. This work deepens into the effect of reaction conditions (450-650 °C, a steam/ethanol (S/E) ratio of 3-9, and a weight space time up to 1.3 h) and evaluates the time on stream evolution of the yields of H2, gaseous byproducts (CO, CO2, CH4, C2H4, C2H4O), and formed carbon/coke. The results are explained taking into consideration the thermodynamics, the extent of each individual reaction, and the catalyst deactivation. Up to 600 °C, the predominant intermediate in the H2 formation is C2H4 (formed by ethanol dehydration) with the preferential formation of nanostructured carbon (nanotubes/filaments) by C2H4 decomposition. The deposition of this type of carbon partially deactivates the catalyst, mainly affecting the extent of the C2H4 decomposition causing a sharp decrease in the H2 and carbon yields. Nevertheless, the catalyst reaches a pseudosteady state with an apparent constant activity for other reactions in the kinetic scheme. At 650 °C, C2H4O (formed by the ethanol dehydrogenation) is the main intermediate in the H2 formation, which is the precursor of an amorphous/turbostratic carbon (coke) formation that initially causes a rapid deactivation of the catalyst, affecting the ethanol dehydration and, to a lower extent, the reforming and water gas shift reactions. The increase in the S/E ratio favors the H2 formation, attenuates the catalyst deactivation due to the suppression of the ethanol dehydration to C2H4, and promotes the reforming, water gas shift, and carbon/coke gasification reactions. A H2 yield of 85% stable for 48 h on stream is achieved at 600 °C, with a space time of 0.1 h and an S/E ratio of 9.

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.

The Route from Green H2 Production through Bioethanol Reforming to CO2 Catalytic Conversion: A Review

Currently, a progressively different approach to the generation of power and the production of fuels for the automotive sector as well as for domestic applications is being taken. As a result, research on the feasibility of applying renewable energy sources to the present energy scenario has been progressively growing, aiming to reduce greenhouse gas emissions. Following more than one approach, the integration of renewables mainly involves the utilization of biomass-derived raw material and the combination of power generated via clean sources with conventional power generation systems. The aim of this review article is to provide a satisfactory overview of the most recent progress in the catalysis of hydrogen production through sustainable reforming and CO2 utilization. In particular, attention is focused on the route that, starting from bioethanol reforming for H2 production, leads to the use of the produced CO2 for different purposes and by means of different catalytic processes, passing through the water–gas shift stage. The newest approaches reported in the literature are reviewed, showing that it is possible to successfully produce “green” and sustainable hydrogen, which can represent a power storage technology, and its utilization is a strategy for the integration of renewables into the power generation scenario. Moreover, this hydrogen may be used for CO2 catalytic conversion to hydrocarbons, thus giving CO2 added value.

Insights into the Reaction Routes for H2 Formation in the Ethanol Steam Reforming on a Catalyst Derived from NiAl2O4 Spinel

This work describes the satisfactory performance of a Ni/Al₂O₃ catalyst derived from NiAl₂O₄ spinel in ethanol steam reforming and focuses on studying the prevailing reaction routes for H₂ formation in this system. NiAl₂O₄ spinel was synthesized using a coprecipitation method and reduced at 850 °C to obtain a Ni/Al₂O₃ catalyst. The spinel structure and catalyst were characterized using XRD, TPR, N₂ physisorption, NH₃ adsorption and TPD, TPO, SEM, and TEM. The experiments were carried out in a fluidized-bed reactor at 500 or 600 °C and different space-time values, using pure ethanol, ethanol-water, pure ethylene, or ethylene-water feeds. The reaction takes place through two paired routes activated by each catalyst function (metal and acid sites) whose extent is limited by the selective catalyst deactivation. The results evidence that at the beginning of the reaction the main route for the formation of H₂ and carbon (nanotubes) is the dehydration of ethanol on acid sites followed by decomposition of ethylene on the Ni-Al₂O₃ interface. This route is favored at 500 °C. After the rapid deactivation of the catalyst for ethylene decomposition, the route of H₂ formation by steam reforming of ethanol and water gas shift reactions over Ni sites is favored. The morphology of the carbon deposits (nanotubes) allows the catalyst to maintain a notable activity for the latter pathways, with stable formation of H₂ (during 48 h in the experiments carried out). At 600 °C, the extent of the gasification reaction of carbon species lowers the carbon material formation. The high formation of carbon material is interesting for the coproduction of H₂ and carbon nanotubes with low CO₂ emissions.

Bioalcohol Reforming: An Overview of the Recent Advances for the Enhancement of Catalyst Stability

The growing demand for energy production highlights the shortage of traditional resources and the related environmental issues. The adoption of bioalcohols (i.e., alcohols produced from biomass or biological routes) is progressively becoming an interesting approach that is used to restrict the consumption of fossil fuels. Bioethanol, biomethanol, bioglycerol, and other bioalcohols (propanol and butanol) represent attractive feedstocks for catalytic reforming and production of hydrogen, which is considered the fuel of the future. Different processes are already available, including steam reforming, oxidative reforming, dry reforming, and aqueous-phase reforming. Achieving the desired hydrogen selectivity is one of the main challenges, due to the occurrence of side reactions that cause coke formation and catalyst deactivation. The aims of this review are related to the critical identification of the formation of carbon roots and the deactivation of catalysts in bioalcohol reforming reactions. Furthermore, attention is focused on the strategies used to improve the durability and stability of the catalysts, with particular attention paid to the innovative formulations developed over the last 5 years.

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.