Issue Date: October 25, 2010
Nanodiamond Catalyst Drives Reaction
Diamond nanoparticles can catalyze a major industrial reaction more effectively and under simpler conditions than the standard commercial transition-metal-based catalyst typically used for that process, according to an international team of researchers (Angew. Chem. Int. Ed., DOI: 10.1002/anie.201002869). The study suggests new avenues for basic research in nonmetal catalytic materials and may lead to improvements in petrochemical processing.
Styrene, a monomer widely used to produce polystyrene and various copolymers, is produced at the billion-pound-per-year level largely from catalytic dehydrogenation of ethylbenzene over a potassium-promoted iron oxide catalyst. To prevent buildup of "coke," a carbonaceous material that deactivates the catalyst, the reaction is carried out at high temperature in the presence of a large volume of steam, making ethylbenzene dehydrogenation an energy-intensive process.
Switching catalysts could reduce the energy needs of that process. Chemists Jian Zhang, Dang Sheng Su, and Robert Schlögl of Fritz Haber Institute, Berlin, and their coworkers in China and Croatia find that acid-treated diamond nanoparticles catalyze ethylbenzene dehydrogenation readily but do not accumulate coke, thereby eliminating the need for steam.
To evaluate the new catalyst, the team compared it with a standard potassium-promoted iron oxide catalyst in the absence of steam. After a few hours' exposure to ethylbenzene, the commercial catalyst's activity dropped rapidly and its surface became coated with coke. In contrast, the nanodiamond surface remained clean after a few days' exposure, and its activity held constant at nearly three times the value of the iron catalyst. The group also found the nanodiamond catalyst to be several times more active than carbon nanotubes, activated carbon, and other carbon materials.
The catalyst's high activity stems from its hybrid structure, the group explains. On the basis of microscopic and spectroscopic analysis, the researchers find that their preparation procedure yields particles with roughly 5-nm cores and a thin, defective graphenelike shell that's functionalized with ketone, diketone, and other oxygen-containing groups that can serve as electron donors and activate ethylbenzene's alkane moiety.
New catalysts that provide excellent performance in workhorse industrial processes always generate interest in the catalysis community, says George J. Antos, a retired industrial chemist who now directs an NSF catalysis program. "While we may reasonably question the likelihood that nanodiamond catalysts will be cost-effective replacements for iron-based catalysts at commercial volumes, the study provides science value that may ultimately lead to new commercial catalysts," he says.
Antos expects that this study will stimulate follow-up work in which the nature and properties of the graphene shell will be targeted for less costly carbon supports or other types of catalysts. He remarks that those studies may eventually lead to replacements for the iron-based styrene catalyst technology.
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