Dimethyl ether (DME) as an alternative fuel

Periodic, self-consistent density functional theory (DFT-GGA) calculations are used to investigate the water gas shift reaction (WGSR) mechanism on Cu(111). The thermochemistry and activation energy barriers for all the elementary steps of the commonly accepted redox mechanism, involving complete water activation to atomic oxygen, are presented. Through our calculations, we identify carboxyl, a new reactive intermediate, which plays a central role in WGSR on Cu(111). The thermochemistry and activation energy barriers of the elementary steps of a new reaction path, involving carboxyl, are studied. A detailed DFT-based microkinetic model of experimental reaction rates, accounting for both the previous and the new WGSR mechanism show that, under relevant experimental conditions, (1) the carboxyl-mediated route is the dominant path, and (2) the initial hydrogen abstraction from water is the rate-limiting step. Formate is a stable “spectator” species, formed predominantly through CO2 hydrogenation. In addition...

On the mechanism of low-temperature water gas shift reaction on copper.

A large number of studies can be found in the literature regarding the production of new catalysts for methanol steam reforming. This work summarizes the latest developments on catalysts for this application and is divided in two main groups: copper-based and group 8–10 metal-based catalysts. In each section, the strategies proposed by several authors to enhance the performance of the catalysts are described. An overall comparison between the two groups shows that copper-based catalysts are the most active ones, while the 8–10 group catalysts present better results in terms of thermal stability and long-term stability. Very promising results were reported for both groups, enhancing the value of methanol as a hydrogen carrier for fuel cell applications.

Catalysts for methanol steam reforming—A review

The progress in water gas shift and steam reforming hydrogen production technologies – A review

The world’s progression towards the Hydrogen economy is facilitating the production of hydrogen from various resources. In the carbon based hydrogen production, Water gas shift reaction is the intermediate step used for hydrogen enrichment and CO reduction in the synthesis gas. This paper makes a critical review of the developments in the modeling approaches of the reaction for use in designing and simulating the water gas shift reactor. Considering the fact that the rate of the reaction is dependent on various parameters including the composition of the catalyst, the active surface and structure of the catalyst, the size of the catalyst, age of the catalyst, its operating temperature and pressure and the composition of the gases, it is difficult to narrow down the expression for the shift reaction. With different authors conducting experiments still to validate the kinetic expressions for the shift reaction, continuous research on different composition and new catalysts are also reported periodically. Moreover the commercial catalyst manufacturers seldom provide information on the catalyst. This makes the task of designers difficult to model the shift reaction. This review provides a consolidated listing of the various important kinetic expressions published for both the high temperature and the low temperature water gas shift reaction along with the details of the catalysts and the operating conditions at which they have been validated.

A Review of the Water Gas Shift Reaction Kinetics

Water gas shift reaction kinetics and reactor modeling for fuel cell grade hydrogen

This paper presents the results of experiments of the methanol decomposition reaction catalyzed by a commercial Cu/ZnO/Al2O3 in the absence and presence of water. Methanol decomposition of 100% in the absence of water was obtained at 290 °C and a space velocity of 2 cm3/h g cat. At these conditions, the hydrogen yield was 1.9–2.0. Water addition to the feed increased the yield of hydrogen and reduced the formation of: dimethyl ether; methyl formate and methane. The variation of the catalyst’s activity and selectivity with time, temperature and feed composition was consistent with previous studies of methanol–steam reforming and water–gas shift reaction, however, this appears to be the first study over the same catalyst of methanol decomposition and methanol–steam reforming. XPS analysis of used catalyst samples and time on-stream data showed that the Cu2+ oxidation state of copper favors methanol decomposition, and we propose that the deactivation of the catalyst is mainly caused by the change in the oxidation state of copper.

Fuel cell grade hydrogen from methanol on a commercial Cu/ZnO/Al2O3 catalyst

Kinetics, simulation and insights for CO selective oxidation in fuel cell applications

Kinetics, simulation and optimization of methanol steam reformer for fuel cell applications

Introduction The advantages of high energy density, easy availability and safe handling/storage are now making methanol one of the most promising sources of hydrogen for fuel cell systems. While extensive work has been done for decades on how to synthesize methanol, recent research is now concentrating on how to produce hydrogen efficiently from methanol. The goal of our work is to maximize hydrogen yield while minimizing the size of the reforming unit. Therefore to design a compact and efficient methanol reformer, reaction data and kinetics are needed for methanol decomposition, methanol-steam reforming and the water gas shift reaction (1~3). CH3OH = CO + 2H2 (1) CH3OH + H2O = CO2 + 3H2 (2) CO + H2O = CO2 + H2 (3) There are few published studies addressing the mechanism and kinetics of methanol decomposition on Cu/ZnO/Al2O3 catalysts. But several groups have studied the mechanism and rate-expression for methanol-steam reforming. An early hypothesis believed that H2/CO formation occurred first followed by the water gas shift reaction. A direct reaction to form CO2 and H2 from methanol was proposed recently. Another report showed that the rates for all three reactions (methanol-steam reforming, water-gas shift reaction and methanol decomposition) must be included in the kinetic analysis. In those mechanisms the rate determining step is either the dehydrogenation of methoxy groups or methyl formate hydrolysis 3, 4, . In spite of the extensive literature on Cu/Zn/Al2O3 catalysts, much remains in dispute concerning the role of the oxidation states of Cu. And also most studies use various x-ray, IR, and TPR/TPD techniques, etc., however, it is hard to find a study which relates the product distribution to the catalyst state. Furthermore, there are few papers, which address the effects of water addition on methanol decomposition. The purpose of our study is to examine the reaction mechanism, by product formation and kinetics of methanol decomposition in the absence and presence of water. Cu oxidation state and its relation to deactivation is also determined through XPS analysis of the catalyst and time-on-stream tests. Rate expressions and kinetic parameters used to fit the experimental data were determined.

Yongtaek Choi

Papers

Water gas shift reaction kinetics and reactor modeling for fuel cell grade hydrogen

Fuel cell grade hydrogen from methanol on a commercial Cu/ZnO/Al2O3 catalyst

Kinetics, simulation and insights for CO selective oxidation in fuel cell applications

Kinetics, simulation and optimization of methanol steam reformer for fuel cell applications

Kinetics of methanol decomposition and water gas shift reaction on a commercial Cu-ZnO/Al2O3 catalyst