This Review describes recent advances in the design, synthesis, reactivity, selectivity, structural, and electronic properties of the catalysts for reforming of a variety of oxygenates (e.g., from simple monoalcohols to higher polyols, then to sugars, phenols, and finally complicated mixtures like bio-oil). A comprehensive exploration of the structure–activity relationship in catalytic reforming of oxygenates is carried out, assisted by state-of-the-art characterization techniques and computational tools. Critical emphasis has been given on the mechanisms of these heterogeneous-catalyzed reactions and especially on the nature of the active catalytic sites and reaction pathways. Similarities and differences (reaction mechanisms, design and synthesis of catalysts, as well as catalytic systems) in the reforming process of these oxygenates will also be discussed. A critical overview is then provided regarding the challenges and opportunities for research in this area with a focus on the roles that systems of ...

Catalytic Reforming of Oxygenates: State of the Art and Future Prospects.

This review reports recent achievements in dimethyl ether (DME) synthesis via CO2 hydrogenation. This gas-phase process could be considered as a promising alternative for carbon dioxide recycling toward a (bio)fuel as DME. In this view, the production of DME from catalytic hydrogenation of CO2 appears as a technology able to face also the ever-increasing demand for alternative, environmentally-friendly fuels and energy carriers. Basic considerations on thermodynamic aspects controlling DME production from CO2 are presented along with a survey of the most innovative catalytic systems developed in this field. During the last years, special attention has been paid to the role of zeolite-based catalysts, either in the methanol-to-DME dehydration step or in the one-pot CO2-to-DME hydrogenation. Overall, the productivity of DME was shown to be dependent on several catalyst features, related not only to the metal-oxide phase—responsible for CO2 activation/hydrogenation—but also to specific properties of the zeolites (i.e., topology, porosity, specific surface area, acidity, interaction with active metals, distributions of metal particles, …) influencing activity and stability of hybridized bifunctional heterogeneous catalysts. All these aspects are discussed in details, summarizing recent achievements in this research field.

https://www.mdpi.com/1420-3049/23/1/31/pdf

CO2 Recycling to Dimethyl Ether: State-of-the-Art and Perspectives

The vapor-phase decomposition of formic acid was studied over Au supported on various materials, with the aim of producing CO-free H2. With regards to the decomposition and H2 formation, Au/SiO2 was found to be the most active catalyst. The reaction started at 373 K and was complete at 523 K. Depending on the nature of the supports, significant differences were experienced in the reaction pathways. On Au deposited on SiO2, CeO2, and carbon Norit, dehydrogenation predominated, whereas on Al2O3, ZSM-5, and TiO2-supported Au, dehydration of formic acid was favored. Pure CO-free H2 was obtained on Au/SiO2 and Au/CeO2 at and below 473 K. No changes in activity or selectivity were observed within ∼10 h. For most of the catalysts, the selectivity was improved by the addition of water to formic acid. In situ infrared spectroscopic studies revealed the formation of formate species even on Au/SiO2, located exclusively on Au particles. The decomposition of HCOOH over Au/SiO2 followed zero-order kinetics. The activat...

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Decomposition and reforming of formic acid on supported Au catalysts: production of CO-free H2

Dimethyl ether synthesis from Victorian brown coal through gasification – Current status, and research and development needs

Hydrogen economy is a situation where hydrogen is used as the major carrier of energy. Proton exchange membrane fuel cells (PEMFCs) are some of the most interesting candidates to cover the necessity of new technologies that use hydrogen as fuel. PEMFCs are fueled by highly pure hydrogen, which is industrially produced as a hydrogen-rich stream mainly via steam reforming of natural gas; it is then further purified to achieve the desired quality. Nowadays, membrane-based processes are considered to be the most promising technologies for the production of high-purity hydrogen. For hydrogen separation, polymeric, metallic, mixed matrix and ceramic membranes have been extensively studied. In this chapter, the principal results and technical advances for hydrogen separation membranes are summarized. H 2 could be selectively removed from the reaction system and higher conversion be obtained even at lower temperatures if the membrane is coupled to catalytic reactors (membrane reactors (MRs)). The use of palladium and silica membranes into MRs is reviewed.

Advances in Hydrogen Separation and Purification with Membrane Technology

The adsorption and reactions of dimethyl ether (DME) were investigated on Au nanoparticles supported by various oxides and carbon Norit. Infrared spectroscopic and temperature programmed desorption studies revealed that DME adsorbs readily on most oxidic supports. A limited dissociation of DME to methoxy species was established on Au particles by IR spectroscopy. As regards the formation of hydrogen, Au/CeO2 is the most effective catalyst. On Au/Al2O3 catalyst the main process was the formation of methanol with a very small amount of hydrogen. Deposition of Au on CeO2–Al2O3 mixed oxide resulted in a very active catalyst for H2 production. The yield for H2 in the reforming of DME approached the value of 73% at 723–773 K. This feature was explained by the hydrolysis of DME to methanol on alumina, and the fast decomposition of methanol at the Au/CeO2 interface. Adding potassium promoter to Au/CeO2–Al2O3 catalyst further enhanced the production of hydrogen as indicated by the increase of the yield to ∼87%. No deactivation of the catalyst was experienced at 773 K for the measured time, ∼10 h.

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I. Ugrai

Papers

Production of hydrogen from dimethyl ether on supported Au catalysts