Dimethyl ether (DME) as an alternative fuel

Catalytic partial oxidation of methane has been reviewed with an emphasis on the reaction mechanisms over transition metal catalysts. The thermodynamics and aspects related to heat and mass transport is also evaluated, and an extensive table on research contributions to methane partial oxidation over transition metal catalysts in the literature is provided. Presented are both theoretical and experimental evidence pointing to inherent differences in the reaction mechanism over transition metals. These differences are related to methane dissociation, binding site preferences, the stability of OH surface species, surface residence times of active species and contributions from lattice oxygen atoms and support species. Methane dissociation requires a reduced metal surface, but at elevated temperatures oxides of active species may be reduced by direct interaction with methane or from the reaction with H, H2, C or CO. The comparison of elementary reaction steps on Pt and Rh illustrates that a key factor to produce hydrogen as a primary product is a high activation energy barrier to the formation of OH. Another essential property for the formation of H2 and CO as primary products is a low surface coverage of intermediates, such that the probability of O–H, OH–H and CO–O interactions are reduced. The local concentrations of reactants and products change rapidly through the catalyst bed. This influences the reaction mechanisms, but the product composition is typically close to equilibrated at the bed exit temperature.

A review of catalytic partial oxidation of methane to synthesis gas with emphasis on reaction mechanisms over transition metal catalysts

The catalytic performance of supported noble metal catalysts for the steam reforming (SR) of ethanol has been investigated in the temperature range of 600–850 °C with respect to the nature of the active metallic phase (Rh, Ru, Pt, Pd), the nature of the support (Al2O3, MgO, TiO2) and the metal loading (0–5 wt.%). It is found that for low-loaded catalysts, Rh is significantly more active and selective toward hydrogen formation compared to Ru, Pt and Pd, which show a similar behavior. The catalytic performance of Rh and, particularly, Ru is significantly improved with increasing metal loading, leading to higher ethanol conversions and hydrogen selectivities at given reaction temperatures. The catalytic activity and selectivity of high-loaded Ru catalysts is comparable to that of Rh and, therefore, ruthenium was further investigated as a less costly alternative. It was found that, under certain reaction conditions, the 5% Ru/Al2O3 catalyst is able to completely convert ethanol with selectivities toward hydrogen above 95%, the only byproduct being methane. Long-term tests conducted under severe conditions showed that the catalyst is acceptably stable and could be a good candidate for the production of hydrogen by steam reforming of ethanol for fuel cell applications.

Production of hydrogen for fuel cells by steam reforming of ethanol over supported noble metal catalysts

Perovskites as substitutes of noble metals for heterogeneous catalysis: dream or reality.

Reaction network of steam reforming of ethanol over Ni-based catalysts

Catalytic reaction of steam reforming of dimethyl ether (DME) to hydrogen-rich gas was studied in a fixed-bed continuous-flow reactor at a temperature of 200–360°C under atmospheric pressure over a mechanical mixture of catalysts for DME hydration and for methanol steam reforming. It was found that the mechanical mixture of 12-tungstosilicoheteropolyacid deposited on γ-Al 2 O 3 (DME hydration catalyst) and copper deposited on SiO 2 (methanol steam reforming catalyst) provided a 100% DME conversion and hydrogen outlet concentration of ∼71 vol.% at 290°C and GHSV ∼1200 h −1 .

Production of hydrogen from dimethyl ether

A two-layer fixed-bed catalytic reactor for syngas production by steam reforming of ethanol has been proposed. In the reactor, ethanol is first converted to a mixture of methane, carbon oxides and hydrogen over a Pd-based catalyst and then this mixture is converted to syngas over a Ni-based catalyst for methane steam reforming. It has been shown that the use of the two-layer fixed-bed reactor prevents coke formation and provides the syngas yield closed to equilibrium.

Synthesis gas production by steam reforming of ethanol

Methane oxidation over Fe-, Co-, Ni- and V-containing mixed conductors

Electrocatalytic oxidation of methane over Pt-based electrode-catalyst in a solid oxide fuel cell reactor CH 4 Pt0.9ZrO 2 +0.1Y 2 O 3 |Pt, air was studied at 800°C and atmospheric pressure. SEM and ESCA techniques were used to characterize the electrode-catalyst. It is found that the Pt-based electrode is an active electrode-catalyst for partial oxidation of methane (in a diluent absence) to syngas, concentration ratio being [H2]/[CO]≈2. Methane conversion and carbon monoxide selectivity attained 97% and 95%, respectively. Under these conditions, reactor is operated in a fuel cell mode and the electrode-catalyst is stable (to coking, too).

G. L. Semin

Papers

Production of hydrogen from dimethyl ether

Synthesis gas production by steam reforming of ethanol

Methane oxidation over Fe-, Co-, Ni- and V-containing mixed conductors

Methane conversion to syngas over Pt-based electrode in a solid oxide fuel cell reactor

Methane oxidation on the surface of mixed-conducting La0.3Sr0.7Co0.8Ga0.2O3-δ