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X I NHE BAO/DA LI A N I NST.
CATALYST IN A TUBE CATALYSIS: Trapping metal particles
inside nanotubes improves their physical and chemical properties
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ONFINING METALLIC nanoparticles inside carbon nanotubes alters the redox properties of the particles and can enhance their effectiveness as catalysts, according to a new study (J. Am. Chem. Soc., DOI: 10.1021/ja8008192). The investigation highlights a novel procedure for tailoring electronic properties of nanoparticles and may lead to various applications in catalysis, gas sensing, and magnetic devices. Carbon nanotubes are similar in some ways to activated carbon, used commercially as a catalyst support, yet they have electronic properties that make them a better support material for some types of reactions. Researchers are particularly interested in the effect of catalyst confinement achieved by attaching particles to interior nanotube surfaces, which differ electronically from nanotube exteriors. Most preparation methods, however, place the particles on the outer surfaces. Now, Xinhe Bao, Xiulian Pan, Wei Chen, and Zhongli Fan at Dalian Institute of Chemical Physics, in China, have shown that a solution-phase method aided by ultrasonication selectively deposits iron oxide nanoparticles inside carbon nanotubes. These particles are precursors for the catalyst used in Fischer-Tropsch (FT) synthesis, a carbon-coupling method for making synthetic fuels from mixtures of CO and hydrogen. The team finds that confined particles are more prone to chemical reduction than particles attached to the exterior of the nanotubes. Specifically, they report that reduction of the particles with hydrogen and CO, which converts the precursors to the working form of
the catalyst, doubles the ratio of iron carbide/iron oxide surface species on catalyst particles inside a nanotube compared with particles on the outside. A high relative concentration of iron carbide species is believed to be essential for high FT activity. In FT synthesis tests, the team monitored the concentration of five-carbon and larger hydrocarbons. They found that, compared with exterior particles and particles supported on activated carbon, nanotubeconfined FT catalyst particles produced twice and six times the yield, respectively. Concerned initially about diffusion limitation problems, the Dalian team developed methods for cutting the tubes into short segments to minimize the distance that reactant and product molecules would need to travel to get in and out of the nanotubes. Judging by the enhanced reducibility of the confined particles, however, Bao notes that diffusion is not a severe impediment. The group now plans to conduct diffusion simulation studies. “This is exciting work,” comments Charles H. F. (Chuck) Peden, a senior scientist at Pacific Northwest National Laboratory. Clearly, there are dramatic differences in the chemical and physical properties of the catalyst particles when they are put inside or outside the nanotube channels, he says.—MITCH JACOBY
Particles of about 5 nm inside carbon nanotubes (left) are more catalytically active than particles on the outside surfaces (right).
GENERIC DRUGS Germany’s Fresenius will acquire heparin leader APP Pharmaceuticals Fresenius, the Berlin-based supplier of hospital, dialysis, and home medical care products, has agreed to acquire APP Pharmaceuticals, a Schaumburg, Ill.-based maker of generic injectable drugs, in a stock deal valued at $3.7 billion. Fresenius also will assume APP’s approximately $940 million in debt. The acquisition gives Fresenius a foothold in the U.S. market for injectable drugs. With 2007 revenues of nearly $650 million, APP manufactures more than 100 hospital-based injectable therapies for oncology, anti-infective, anesthetic/analgesic, and critical care
markets. It became the lead supplier of heparin, a key blood-thinning agent for patients on dialysis, after the recent recall of Baxter International’s heparin product. APP also will add a generic drug portfolio to the German firm’s product line at a time when major pharmaceutical firms are looking to diversify their offerings with generics. Last month, for example, Japan’s Daiichi Sankyo said it would acquire the Indian generics firm Ranbaxy Laboratories (C&EN, June 16, page 14). Within Fresenius, APP will join the Fresenius Kabi infusions division. “The
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acquisition provides significant growth opportunities for Fresenius Kabi,” says Ulf Mark Schneider, chairman of Fresenius’ management board. “With the APP platform, Fresenius Kabi will be able to market its product range in the U.S.” The new deal is part of a general trend among drug companies to integrate generics into their existing operations, says Viren Mehta, founder of biopharma financial advisers Mehta Partners, which counseled Daiichi in the Ranbaxy acquisition. “Any company that wants to survive, if not prosper, will have to look at the entire value chain,” he says.—RICK MULLIN
