Catalysis research of relevance to carbon management: progress, challenges, and opportunities.

The goal of the "Opportunities for Catalysis Research in Carbon Management" workshop was to review within the context of greenhouse gas/carbon issues the current state of knowledge, barriers to further scientific and technological progress, and basic scientific research needs in the areas of H2 generation and utilization, light hydrocarbon activation and utilization, carbon dioxide activation, utilization, and sequestration, emerging techniques and research directions in relevant catalysis research, and in catalysis for more efficient transportation engines. Several overarching themes emerge from this review. First and foremost, there is a pressing need to better understand in detail the catalytic mechanisms involved in almost every process area mentioned above. This includes the structures, energetics, lifetimes, and reactivities of the species thought to be important in the key catalytic cycles. As much of this type of information as is possible to acquire would also greatly aid in better understanding perplexing, incomplete/inefficient catalytic cycles and in inventing new, efficient ones. The most productive way to attack such problems must include long-term, in-depth fundamental studies of both commercial and model processes, by conventional research techniques and, importantly, by applying various promising new physicochemical and computational approaches which would allow incisive, in situ elucidation of reaction pathways. There is also a consensus that more exploratory experiments, especially high-risk, unconventional catalytic and model studies, should be undertaken. Such an effort will likely require specialized equipment, instrumentation, and computational facilities. The most expeditious and cost-effective means to carry out this research would be by close coupling of academic, industrial, and national laboratory catalysis efforts worldwide. Completely new research approaches should be vigorously explored, ranging from novel compositions, fabrication techniques, reactors, and reaction conditions for heterogeneous catalysts, to novel ligands and ligation geometries (e.g., biomimetic), reaction media, and activation methods for homogeneous ones. The interplay between these two areas involving various hybrid and single-site supported catalyst systems should also be productive. Finally, new combinatorial and semicombinatorial means to rapidly create and screen catalyst systems are now available. As a complement to the approaches noted above, these techniques promise to greatly accelerate catalyst discovery, evaluation, and understanding. They should be incorporated in the vigorous international research effort needed in this field.

A mercury-catalyzed, high-yield system for the oxidation of methane to methanol.

A homogeneous system for the selective, catalytic oxidation of methane to methanol via methyl bisulfate is reported. The net reaction catalyzed by mercuric ions, Hg(II), is the oxidation of methane by concentrated sulfuric acid to produce methyl bisulfate, water, and sulfur dioxide. The reaction is efficient. At a methane conversion of 50 percent, 85 percent selectivity to methyl bisulfate ( approximately 43 percent yield; the major side product is carbon dioxide) was achieved at a molar productivity of 10(-7) mole per cubic centimeter per second and Hg(II) turnover frequency of 10(-3) per second. Separate hydrolysis of methyl bisulfate and reoxidation of the sulfur dioxide with air provides a potentially practical scheme for the oxidation of methane to methanol with molecular oxygen. The primary steps of the Hg(II)-catalyzed reaction were individually examined and the essential elements of the mechanism were identified. The Hg(II) ion reacts with methane by an electrophilic displacement mechanism to produce an observable species, CH(3)HgOSO(3)H, 1. Under the reaction conditions, 1 readily decomposes to CH(3)OSO(3)H and the reduced mercurous species, Hg(2)(2+) The catalytic cycle is completed by the reoxidation of Hg(2)(2+) with H(2)SO(4) to regenerate Hg(II) and byproducts SO(2) and H(2)O. Thallium(III), palladium(II), and the cations of platinum and gold also oxidize methane to methyl bisulfate in sulfuric acid.

Pharmacologic characterization of acute chlordiazepoxide dependence in the rat.

A single intoxicating dose of chlordiazepoxide HCl (p.o.) in the rat can induce quantifiable manifestations of physical dependence. Dependence was revealed by antagonist precipitation (Ro 15-1788, CGS-8216) as well as spontaneous emergence of neurobehavioral signs of withdrawal observed by multiple raters blind to treatments. Ro 15-1788 was 45% more effective than CGS-8216 in both reversing chlordiazepoxide intoxication and expressing withdrawal signs. The severity of Ro 15-1788-precipitated withdrawal varied with chlordiazepoxide dose, Ro 15-1788 dose and the agonist-antagonist dose interval. Maximal precipitated dependence was evoked 3 days after chlordiazepoxide HCl (450 mg/kg) by Ro 15-1788 (25 mg/kg i.p.). The precipitated syndrome consisted of tail erection, reduced motor activity, high step, curled claw, arched back, muscle hypertonus and piloerection. Ro 15-1788-precipitated dependence emerged between 28 and 52 hr, peaked at 76 hr and disappeared by 124 hr. Spontaneous withdrawal had emerged from 100 to 124 hr and then faded gradually. The neurobehavioral expression of central nervous system depression and its reversal were necessary but not sufficient conditions for the induction and expression of acute chlordiazepoxide dependence. These results suggest caution in reviving acute benzodiazepine-overdosed patients to avoid iatrogenic withdrawal analogous to naloxone for opiates.