Dry (CO2) reforming of methane (DRM) is a well-studied reaction that is of both scientific and industrial importance. This reaction produces syngas that can be used to produce a wide range of products, such as higher alkanes and oxygenates by means of Fischer–Tropsch synthesis. DRM is inevitably accompanied by deactivation due to carbon deposition. DRM is also a highly endothermic reaction and requires operating temperatures of 800–1000 °C to attain high equilibrium conversion of CH4 and CO2 to H2 and CO and to minimize the thermodynamic driving force for carbon deposition. The most widely used catalysts for DRM are based on Ni. However, many of these catalysts undergo severe deactivation due to carbon deposition. Noble metals have also been studied and are typically found to be much more resistant to carbon deposition than Ni catalysts, but are generally uneconomical. Noble metals can also be used to promote the Ni catalysts in order to increase their resistance to deactivation. In order to design catalysts that minimize deactivation, it is necessary to understand the elementary steps involved in the activation and conversion of CH4 and CO2. This review will cover DRM literature for catalysts based on Rh, Ru, Pt, and Pd metals. This includes the effect of these noble metals on the kinetics, mechanism and deactivation of these catalysts.

A review of dry (CO2) reforming of methane over noble metal catalysts

The recent developments and trends in combustion science towards the synthesis of nanomaterials are discussed. Different modifications made to conventional combustion approaches for preparation of nanomaterials are critically analyzed. Special attention is paid to various applications of combustion synthesized nanosized products.

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Combustion synthesis and nanomaterials

Solution combustion is an exciting phenomenon, which involves propagation of self-sustained exothermic reactions along an aqueous or sol–gel media. This process allows for the synthesis of a variety of nanoscale materials, including oxides, metals, alloys, and sulfides. This Review focuses on the analysis of new approaches and results in the field of solution combustion synthesis (SCS) obtained during recent years. Thermodynamics and kinetics of reactive solutions used in different chemical routes are considered, and the role of process parameters is discussed, emphasizing the chemical mechanisms that are responsible for rapid self-sustained combustion reactions. The basic principles for controlling the composition, structure, and nanostructure of SCS products, and routes to regulate the size and morphology of the nanoscale materials are also reviewed. Recently developed systems that lead to the formation of novel materials and unique structures (e.g., thin films and two-dimensional crystals) with unusual...

Solution Combustion Synthesis of Nanoscale Materials

The demand for petroleum has been rising rapidly due to increasing industrialization and modernization. This economic development has led to a huge demand for energy, most of which is derived from fossil fuel. However, the limited reserve of fossil fuel has led many researchers to look for alternative fuels which can be produced from renewable feedstock. Increasing fossil fuel prices have prompted the global oil industry to look at biodiesel, which is from renewable energy sources. Biodiesel is produced from animal fats and vegetable oils and has become more attractive because it is more environmentally friendly and is obtained from renewable sources. Glycerol is the main by-product of biodiesel production; about 10% of the weight of biodiesel is generated in glycerol. The large amount of glycerol generated may become an environmental problem, since it cannot be disposed of in the environment. In this paper, an attempt has been made to review the different approaches and techniques used to produce glycerol (hydrolysis, transesterification, refining crude glycerol). The world biodiesel/glycerol production and consumption market, the current world glycerin and glycerol prices as well as the news trends for the use of glycerol mainly in Brazil market are analyzed. The technological production and physicochemical properties of glycerol are described, as is the characterization of crude glycerol obtained from different seed oil feedstock. Finally, a simple way to use glycerol in large amounts is combustion, which is an advantageous method as it does not require any purification. However, the combustion process of crude glycerol is not easy and there are technological difficulties. The news and mainly research about the combustion of glycerol was also addressed in this review.

Glycerol: Production, consumption, prices, characterization and new trends in combustion

Valorization of native birch wood lignin into monomeric phenols over nickel-based catalysts has been studied. High chemoselectivity to aromatic products was achieved by using Ni-based catalysts and common alcohols as solvents. The results show that lignin can be selectively cleaved into propylguaiacol and propylsyringol with total selectivity >90% at a lignin conversion of about 50%. Alcohols, such as methanol, ethanol and ethylene glycol, are suitable solvents for lignin conversion. Analyses with MALDI-TOF and NMR show that birch lignin is first fragmented into smaller lignin species consisting of several benzene rings with a molecular weight of m/z ca. 1100 to ca. 1600 via alcoholysis reaction. The second step involves the hydrogenolysis of the fragments into phenols. The presence of gaseous H2 has no effect on lignin conversion, indicating that alcohols provide active hydrogen species, which is further confirmed by isotopic tracing experiments. Catalysts are recycled by magnetic separation and can be reused four times without losing activity. The mechanistic insights from this work could be helpful in understanding native lignin conversion and the formation of monomeric phenolics via reductive depolymerization.

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Lignin depolymerization (LDP) in alcohol over nickel-based catalysts via a fragmentation–hydrogenolysis process

Carbon formation and its influence on ethanol steam reforming over Ni/Al2O3 catalysts

Ni and Pt catalysts supported on α-Al2O3, α-Al2O3-ZrO2 and ZrO2 were studied in the dry reforming of methane to produce synthesis gas. All catalytic systems presented well activity levels with TOF (s−1) values between 1 and 3, being Ni based catalysts more active than Pt based catalysts. The selectivity measured at 650 °C, expressed by the molar ratio H2/CO reached values near to 1. Concerning stability, Pt/ZrO2, Pt/α-Al2O3-ZrO2 and Ni/α-Al2O3-ZrO2 systems clearly show lower deactivation levels than Ni/ZrO2 and Ni or Pt catalysts supported on α-Al2O3. The lowest deactivation levels observed in Ni and Pt supported on α-Al2O3-ZrO2, compared with Ni and Pt supported on α-Al2O3 can be explained by an inhibition of reactions leading to carbon deposition in systems having ZrO2. These results suggest that ZrO2 promotes the gasification of adsorbed intermediates, which are precursors of carbon formation and responsible for the main deactivation mechanism in dry reforming reaction.

Study of Ni and Pt catalysts supported on α-Al2O3 and ZrO2 applied in methane reforming with CO2

Reforming of Methane with Carbon Dioxide over Pt/ZrO2/Al2O3 Catalysts

Biodiesel production from soybean oil and methanol using hydrotalcites as catalyst

Autothermal reforming of methane, combining steam reforming and partial oxidation was carried out with Pt/Al2O3, Pt/ZrO2 and Pt/ZrO2/Al2O3 catalysts, in the temperature range of 400–900 °C. The Pt/ZrO2/Al2O3 catalyst was found to be the most active and stable at 800 °C due to the higher resistance to coke formation. The reaction occurs in two simultaneous stages: total combustion of methane and reforming of the unconverted methane with steam and CO2, with the O2 conversion of 100% starting from 450 °C. The addition of O2 to the feed increases methane conversion and the catalyst stability, decreasing the H2 and CO yields due to the enhancement of methane combustion. By manipulating the O2/CH4 ratio of the feed it is possible to achieve the H2/CO ratio that is optimal to the GTL processes.

Mariana M.V.M. Souza

Papers

Carbon formation and its influence on ethanol steam reforming over Ni/Al2O3 catalysts

Study of Ni and Pt catalysts supported on α-Al2O3 and ZrO2 applied in methane reforming with CO2

Reforming of Methane with Carbon Dioxide over Pt/ZrO2/Al2O3 Catalysts

Biodiesel production from soybean oil and methanol using hydrotalcites as catalyst

Autothermal reforming of methane over Pt/ZrO2/Al2O3 catalysts