Catalytic Catamarans: Common industrial catalyst sports rafts made of platinum
The study shows that the aluminum atoms in the material support for another bond thirst grabs platinum and anchor. The anchors allow atoms of platinum group on rafts that float above the support surface, providing ample space for the catalytic reactions.
Researchers at the Institute for Interfacial Catalysis at the Department of Energy’s Pacific Northwest National Laboratory and the Department of Energy at Oak Ridge National Laboratory has conducted an analysis of industrial catalysts known as aluminum oxide and platinum support. Precious metals and oxide combinations are the most common type of industrial catalysts. The new work will help engineers to monitor the preparation of the catalyst, leading to performance improvements.
“We were able to specifically identify an important site for the anchoring of platinum on the surface of aluminum oxide formed during synthesis,” said PNNL chemist Chuck Peden and co-author. “While platinum rafts have been observed before, this is the first time we had a clear vision at the molecular level the processes that create them.”
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In these catalysts, the oxides are simply a surface on which precious metal feel, while the breakdown of metals and form bonds in other molecules, such as those found in automobile exhaust. The most efficient catalysts of precious metals spread evenly over the surface of the oxide. The inefficient are the atoms of a precious metal ball into groups, with atoms in the interior is not available for work on the incoming molecules.
Chemists working with gamma-alumina supports and metal platinum knew that under certain conditions, the rafts of platinum atoms could form on the surface oxide. Unlike the balls of atoms, the rafts present most of its residents for the atoms of the incoming molecules, making them desirable structures. But to control the production of the rafts, the team had to learn how they formed.
To find out, the team used powerful tools at EMSL, DOE’s Environmental Molecular Sciences Laboratory on the PNNL campus, and high temperature materials laboratory at ORNL. The team prepared gamma aluminum oxide synthesis conditions considered typical catalyst and support material before and after the addition of platinum.
First, they examined the chemical nature of the support at EMSL, which houses one of the world’s largest instrument of its kind – a 900-megahertz nuclear magnetic resonance (NMR) spectrometer. MRI provided an unprecedented resolution of the aluminum oxide support, which enabled the team to identify the aluminum atoms with certain properties. By its chemical nature, the aluminum atoms prefer to be compelled to four or six atoms. The team found, in the absence of platinum, some were bound for five uncomfortable.
Adding to the mix of platinum, however, caused the number of aluminum atoms with five bonds to decrease and the number of atoms with six links to increase. The number of four bonded atoms remained constant, suggesting that the platinum atoms on the sites of attachment to the aluminum atoms that comes through here, five bonded, called Penta sites.
The team discovered that could increase the number of sites penta raising the temperature during the synthesis of catalysts. More sites means more penta platinum atoms attached to aid.
After finding anchor points, zoom team of aberration-corrected JEOL 2200FS microscope, which can discern individual atoms of platinum in HTML. At low metal concentrations, individual platinum atoms shown as bright spots scattered across the dark surface. At higher concentrations, the image reveals platinum rafts could be seen above the aluminum oxide.
Finally, the team showed that penta-aluminum atoms needed to form rafts. Alpha-alumina Penta contains no sites. When the researchers analyzed under the microscope as a catalyst material with alpha-aluminum oxide, platinum atoms formed around the balls wobbled on the surface rather than ordered rafts.
The theoretical analysis that takes into account all the experimental data gave a model of how forms of catalyst material. The results allow us to understand how there could be a better catalyst performance.
“This knowledge suggests that we have gained some additional tricks you could play for better dispersion of platinum atoms,” said Peden. “For example, if we can find the conditions under which we can add the high-temperature platinum on a larger scale this experiment, then we would have more anchor sites available.”
Find the conditions that allow the chemical to control the number and distribution of penta sites will be subject to future research.
More information: Ja Hun Kwak, Jianzhi Hu, Donghai Mei, Cheol-Woo Yi, Do Heui Kim, Charles H.F. Peden, Lawrence F. Allard and Janos Szanyi, Co-ordinatively unsaturated Al3+ centers as binding sites for active catalyst phases on γ-Al2O3, Science, DOI 10.1126/science.1176745
Source: Pacific Northwest National Laboratory (web)
Tags: aluminum, aluminum atoms, aluminum oxide, atoms, catalyst, catalysts, conditions, form, formed, individual platinum atoms, laboratory, material, metal, oxide, penta, penta sites, platinum, platinum atoms, precious, rafts, sites, supporting, surface, team