(359c) Large-Scale Preparation of Highly Dispersed Pt Nano-Particles On Mesporous Silica Gel by ALD
Nano-particulate platinum has been well-dispersed onto large quantities of micron-sized mesoporous silica gel using Atomic Layer Deposition in a Fluidized Bed Reactor (i.e. ALD-FBR). Transmission Electron Microscopy (TEM) cross-section investigations showed that the Pt nanoparticles are homogeneously distributed throughout primary 30-75µm silica gel particles , including the inner surface comprising 5-7nm pores. A narrow particles size distribution is maintained across the entire substrate. The Pt catalyst loading level is tightly controlled by the number of ALD coating cycles. An extremely low Pt loading with 0.03mg Pt/cm2 and 0.23mg Pt/cm2 was prepared using 3 and 10 ALD coating cycles respectively. The Pt particles size is approximately 1.3nm for 3 ALD coating cycles. For 10 ALD coating cycles, the Pt particle size is measured to be about 2.4 nm. The sample with a 0.03 mg Pt/cm2 loading shows the highest metal dispersion of 90%, i.e. the highest values ever seen in the literature measured by using the H2 chemical absorption method. Metal dispersion is 46% for a 0.23 mg Pt/cm2loading. Thermal stability studies indicate that there is an initial agglomeration of the Pt clusters during the first 4 hours' of heat treatment at 450°C. The particle size increased from 1.3 nm to about 2nm for 3 cycles Pt coated silica gel. After that there is no noticeable change of the particle size during the following heat treatment process. This study shows that the ALD-FBR method is a rational procedure for the low-cost, simple, and scalable preparation of highly dispersed supported catalysts. The mesoporous substrate not only helps to improve the surface activity of the catalyst, but also stabilizes the Pt nano-particles due to its extremely high surface area and tortuous structure.