Effects of Drying Conditions on the Synthesis of Co/SiO2 and Co/Al2O3 Fischer鈥揟ropsch Catalysts
详细信息 查看全文
- 作者：Peter Munnik ; Nynke A. Krans ; Petra E. de Jongh ; Krijn P. de Jong
- 刊名：ACS Catalysis
- 出版年：2014
- 出版时间：September 5, 2014
- 年：2014
- 卷：4
- 期：9
- 页码：3219-3226
- 全文大小：494K
- ISSN：2155-5435
文摘
The nanoscale distribution of the supported metal phase is an important property for highly active, selective, and stable catalysts. Here, the nanoscale redistribution and aggregate formation of cobalt nitrate during the synthesis of supported cobalt catalysts were studied. Drying over a range of temperatures in stagnant air resulted in cobalt particles (8 nm) present in large aggregates (30鈥?50 nm). However, drying in a N2 flow resulted in cobalt nanoparticles distributed either in aggregates or uniformly on various SiO2 and 纬-Al2O3 supports, critically dependent on the drying temperature. The mechanism of aggregation was studied through chemical immobilization of the precursor on a silica support after drying in a N2 flow. The aggregation behavior upon drying in a gas flow at temperatures below 100 掳C showed a remarkable similarity to distributions obtained upon the dewetting of colloidal films, suggesting a physical process. Alternatively, by inducing decomposition of the cobalt nitrate above 100 掳C before drying was complete, aggregation was brought about through a chemical process that occurred both in stagnant and flowing gas. A 纬-alumina support exhibited increased precursor-support interactions and displayed little cobalt aggregation upon drying in a gas flow but extensive aggregation upon drying in stagnant air. The aggregation behavior was further tested on silica supports with pore sizes between 3 and 15 nm and tested under industrially relevant Fischer鈥揟ropsch conditions, which revealed that uniform cobalt nanoparticle distributions were up to 50% more active compared to aggregated systems. Thus, hydrodynamics and the temperature of the gas phase are critical parameters to control nanoscale distributions during drying of functional nanomaterials such as supported catalysts.