There is increased recognition by the world’s scientific, industrial, and political communities that the concentrations of greenhouse gases in the earth’s
atmosphere, particularly CO_2, are increasing. For
example, recent studies of Antarctic ice cores to
depths of over 3600 m, spanning over 420 000 years,
indicate an 80 ppm increase in atmospheric CO_2 in
the past 200 years (with most of this increase
occurring in the past 50 years) compared to the
previous 80 ppm increase that required 10 000 years.2
The 160 nation Framework Convention for Climate
Change (FCCC) in Kyoto focused world attention on
possible links between CO2 and future climate change
and active discussion of these issues continues.3 In
the United States, the PCAST report4 “Federal
Energy Research and Development for the Challenges
of the Twenty First Century” focused attention
on the growing worldwide demand for energy and the
need to move away from current fossil fuel utilization.
According to the U.S. DOE Energy Information
Administration,5 carbon emission from the transportation
(air, ground, sea), industrial (heavy manufacturing,
agriculture, construction, mining, chemicals,
petroleum), buildings (internal heating, cooling, lighting),
and electrical (power generation) sectors of the
World economy amounted to ca. 1823 million metric
tons (MMT) in 1990, with an estimated increase to
2466 MMT in 2008-2012 (Table 1).

Catalysis Research of Relevance to Carbon Management: Progress, Challenges, and Opportunities

Several novel synthetic reactions of arenes and alkanes discovered and investigated in our laboratory are summarized here. These include olefin arylation, hydroarylation of alkynes, hydroxylation of arenes, carboxylation of arenes and alkanes, and aminomethylation and acetoxylation of alkanes. Most of these reactions are catalyzed by highly electrophilic transition metal cationic species generated in situ in an acid medium, involving electrophilic metalation of C−H bonds of arenes and alkanes which lead to the formation of aryl−metal and alkyl−metal σ-complexes.

Catalytic functionalization of arenes and alkanes via C-H bond activation.

Fuel processing for low-temperature and high-temperature fuel cells: Challenges, and opportunities for sustainable development in the 21st century

Hydrogen production reactions from carbon feedstocks: fossil fuels and biomass.

This review describes a number of different, largely catalytic approaches for producing H2. Since a major fraction of the world's H2 is produced by catalytic processes, involving multiple steps with different types of catalysts, it is clear that catalysis plays a critical role in the production of H2. This review is focused on the use of catalysis for the current and future production of H2. Some background will be provided to give a perspective of the dramatic change in the supply and demand for H2 in the past decade, followed by a review of how it is produced commercially, with a view to how multiple types of catalysis contribute to the total process for H2 production. Steam methane reforming, the major approach for H2 manufacture, will be a focal point for most of the discussion in pointing out the large number of catalytic steps that are used in this major technology. Finally, some alternative catalytic approaches for H2 production will be described.

The multiple roles for catalysis in the production of H2

The reaction between methane and oxygen over platinum and rhodium surfaces in metalcoated ceramic monoliths can be made to produce mostly hydrogen and carbon monoxide (greater than 90% selectivity for both) with almost complete conversion of methane and oxygen at reaction times as short as 10–3 seconds. This process has great promise for conversion of abundant natural gas into liquid products such as methanol and hydrocarbons, which can be easily transported from remote locations. Rhodium was considerably superior to platinum in producing more H2 and less H2O, which can be explained by the known chemistry and kinetics of reactants, intermediates, and products on these surfaces.

https://science.sciencemag.org/content/sci/259/5093/343.full.pdf

Production of Syngas by Direct Catalytic Oxidation of Methane

Synthesis gas formation by direct oxidation of methane over Pt monoliths

The direct oxidation of CH4 to H2 and CO in O2 and in air at high temperatures over alumina foam monoliths coated with high loadings of Pt and Rh has been simulated using a 19-elementary-step model of adsorption, desorption and surface reaction steps with reaction parameters from the literature or from fits to previous experiments. The surface reaction model for Pt is in good agreement with previously reported low-pressure(0.1 to 1 torr) reactor measurements of CH4 oxidation rates at temperatures from 600 to 1,500 K and of OH radical desorption during CH4 oxidation at 1,300 to 1,600 K over polycrystalline Pt foils. The model predictions for both catalysts are also consistent with product selectivities observed over monolithic catalysts in an atmospheric-pressure laboratory-scale reactor, and the differences between Pt and Rh can be explained by comparing individual reaction steps on these surfaces. Because of the good agreement between the model and both low-and atmospheric-pressure reactor simulations, a complete energy diagram for methane oxidation at low coverages is proposed. The model results show that under CH4rich conditions at high temperatures, H2 and CO are primary products of the direct oxidation of methane via a pyrolysis mechanism.

Steps in CH4 oxidation on Pt and Rh surfaces: High‐temperature reactor simulations

The production of H2 and CO by catalytic partial oxidation of CH4 in air or O2 at atmospheric pressure has been examined over Rh-coated monoliths at residence times between 10−4 and 10−2 s and compared to previously reported results for Pt-coated monoliths. Using O2, selectivities for H2 (
 
$$S_{H_2 }$$

 ) as high as 90% and CO selectivities (S
CO) of 96% can be obtained with Rh catalysts. With room temperature feeds using air, Rh catalysts give
 
$$S_{H_2 }$$

 of about 70% compared to only about 40% for Pt catalysts. The optimal selectivities for either Pt or Rh can be improved by increasing the adiabatic reaction temperature by preheating the reactant gases or using O2 instead of air. The superiority of Rh over Pt for H2 generation can be explained by a methane pyrolysis surface reaction mechanism of oxidation at high temperatures on these noble metals. Because of the higher activation energy for OH formation on Rh (20 kcal/mol) than on Pt (2.5 kcal/mol), H adatoms are more likely to combine and desorb as H2 than on Pt, on which the O+ H→ OH reaction is much faster.

Synthesis gas formation by direct oxidation of methane over Rh monoliths

Steady state, isotopic, and chemical transient studies of ethanol dehydration on γ-alumina show unimolecular and bimolecular dehydration reactions of ethanol are reversibly inhibited by the formation of ethanol–water dimers at 488 K. Measured rates of ethylene synthesis are independent of ethanol pressure (1.9–7.0 kPa) but decrease with increasing water pressure (0.4–2.2 kPa), reflecting the competitive adsorption of ethanol–water dimers with ethanol monomers; while diethyl ether formation rates have a positive, less than first order dependence on ethanol pressure (0.9–4.7 kPa) and also decrease with water pressure (0.6–2.2 kPa), signifying a competition for active sites between ethanol–water dimers and ethanol dimers. Pyridine inhibits the rate of ethylene and diethyl ether formation to different extents verifying the existence of acidic and nonequivalent active sites for the dehydration reactions. A primary kinetic isotope effect does not occur for diethyl ether synthesis from deuterated ethanol and onl...

Daniel A. Hickman

Papers

Production of Syngas by Direct Catalytic Oxidation of Methane

Synthesis gas formation by direct oxidation of methane over Pt monoliths

Steps in CH4 oxidation on Pt and Rh surfaces: High‐temperature reactor simulations

Synthesis gas formation by direct oxidation of methane over Rh monoliths

Kinetics and Mechanism of Ethanol Dehydration on γ-Al2O3: The Critical Role of Dimer Inhibition