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马自达宣布新一代汽车尾气催化转化器——贵金属使用量大大降低
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Mazda Motor Corporation has unveiled a new generation of catalytic converters that use 70 to 90 per cent less of the precious metals which help to purify exhaust emissions. The converters rely on nanoparticles of the catalytic metal, each less than five nanometres across, studded onto the surface of tiny ceramic spheres. The Japanese firm claims this is the first time 'a catalyst material has been achieved that features single, nanosized precious metal particles embedded in fixed positions.'  The nanoparticle-studded ceramic sphere could cut the use of platinum-group metals in catalytic converters © Mazda Automotive catalysts use platinum, rhodium and palladium to speed up chemical reactions of pollutants such as nitrogen oxide, carbon monoxide and hydrocarbons, to create non-toxic emissions. By using nanoparticles of the precious metals instead of larger particles, less metal is needed to produce the same surface area over the ceramic base of the catalyst. This simple concept had not been utilized in the past because exhaust heat can make the nanoparticles migrate over the surface of the ceramic bead, agglomerating into larger particles, explained Michael Zins, deputy director of the Fraunhofer Institute for Ceramic Technologies and Systems (IKTS) in Dresden, Germany. This reduces the overall surface area of the metal, cutting the converter's efficiency. Mazda reckons it has overcome the agglomeration problem by embedding the precious metal nanoparticles into the ceramic in fixed positions - but it's not saying how. 'Mazda is not giving any technological idea how they are doing it.,' Zins told Chemistry World. 'They are only saying, "We have the technology to do it."' Jochen Münzinger, Mazda spokesman in Germany, would say only that Mazda has worked on the technology for 4 years. He also declined to discuss commercial details or timelines, saying only: 'We intend to put this new catalyst to practical use in the near future, but we cannot disclose which car adopts this first.' Major development Zins described the use of nanoparticles to produce catalysts as a major development, and one that all automakers would like to copy. 'I am sure all other companies are working on the technology,' he said. Indeed, Mazda's claim comes just two months after rival Japanese automaker Nissan announced it had developed a nanotechnology-based catalyst that would cut its precious metals usage by 50 per cent. Nissan, which will share the technology with French partner Renault, intends to launch a new vehicle using the catalyst in late 2008 or early 2009. The chief benefit of the technology is cost savings, Zins said. Vehicle manufacturers use a large proportion of the world's annual platinum, rhodium and palladium output, and the development could eventually have a big impact on the prices of these metals. Less platinum and palladium in catalysts could also translate into health benefits. For example, ongoing research suggests that emissions of platinum-group metals from catalytic converters along US highways might be a root cause of an alarming rise in allergies and asthma. Ned Stafford Source: Chemistry World. 大概意思： 汽车尾气净化催化剂一般是贵金属负载在高热稳定性的载体之上，但是目前贵金属的用量还是比较高，为此汽车尾气净化催化剂的的一个热点问题就是：降低贵金属的含量、提高催化剂的热稳定性！ 对于负载型贵金属催化剂来说，一般而言，如果贵金属的颗粒越小，如果达到相同催化效果的话所用的贵金属就越低！ 但是贵金属颗粒如果很小的话，将导致另外一个问题：贵金属颗粒团聚、向催化剂表面迁移、流速！对于汽车尾气净化催化剂来说，催化剂面临苛刻的使用条件：高温、尾气组分变化不定，因而存在矛盾，相互制约，一直使得贵金属的含量不能降下来。 马自达公司近日（10-10）宣称他们已经找到了很好的方法，制备纳米贵金属并负载于高稳定性的载体之上（克服了贵金属团聚的问题），降低贵金属颗粒大小从而减少贵金属的用量！但是他们并没有透漏任何技术相关的信息！ 本文引用地址：http://www.sciencenet.cn/blog/user_content.aspx?id=8918 |
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