February 23, 2009 Volume 87, Number 08 p. 8

Catalysis

Making Hydrogen Peroxide Directly

Acid treatment of catalyst support could simplify production of chemical

PRETREATING THE SUPPORT for a gold-palladium catalyst used to produce hydrogen peroxide from H 2 and O 2 could provide a simpler, more direct method than that now used to prepare the commodity chemical, reports a research group led by Graham J. Hutchings, a professor of chemistry at Cardiff University, in Wales (Science 2009, 323, 1037).

Graham Hutchings/Cardiff U Direct Conversion Au-Pd nanoparticles, typically smaller than 10 nm in diameter, on an acid-treated activated carbon support can hydrogenate O 2 into H 2 O 2 while producing little H 2 O. Carbon support is gray, Au is yellow, Pd is blue, O is red, and H is white.

H 2 O 2 is used commercially for disinfection and bleaching; the global market for the chemical is expected to reach 3.8 million tons this year, according to a 2008 report by Global Industry Analysts. The current method to produce H 2 O 2 is an indirect process that involves sequential hydrogenation and oxidation of an anthraquinone. Direct methods tend not just to hydrogenate O 2 into H 2 O 2 but also to convert H 2 O 2 into water.

Hutchings and colleagues, however, have now found that pretreating an activated carbon support with either nitric or acetic acid, then drying the support before adding gold and palladium, results in a reusable catalyst that produces H 2 O 2 with minimal conversion to H 2 O.

Drawing from a combination of hydrogenation experiments and scanning transmission electron microscopy of prepared catalysts, the researchers propose that acid pretreatment of the catalyst support leads to smaller and better dispersed Au-Pd nanoparticles. The improved nanoparticle dispersion somehow shuts down sites that would convert H 2 O 2 into water, they suggest.

More work needs to be done to evaluate the effect of acid pretreatment for H 2 O 2 synthesis under conditions that more closely mimic a manufacturing setting, Hutchings says.

Nevertheless, "these are intriguing results showing that hydrogen peroxide can be made with high selectivity via a direct process," says D. Wayne Goodman, a chemistry professor at Texas A&M University. "This disclosure will no doubt promote an active search to identify the underlying cause or causes for this spectacular yet poorly understood effect."