Novel and Effective Copper–Aluminum Propane Dehydrogenation Catalysts

The importance of solid catalysts for converting petroand bulk chemicals is reflected in the sheer magnitude of their market size: catalysts sales topped nine billion dollars in 2009. This large value mirrors also the increasing academic interest in heterogeneous catalysis research. As far as bulk chemicals (such as ethene, propene, and their derivatives) are concerned, there is a strong demand for clean and inexpensive catalysts and synthesis processes. There are two types of commonly used dehydrogenation catalysts: supported Cr oxides and Ptbased systems. The problem is that these catalysts are typically either rare and costly, or hazardous. Moreover, they perform well only at high temperatures (typically at 500–600 8C) due to thermodynamic limitations. Optimization studies have led to the inclusion of several promoters of which tin, especially in the combination with platinum as Pt–Sn/ Al2O3 is one of the most popular. We report here the discovery of a new alternative catalyst for propane dehydrogenation which does not contain noble or hazardous metals. It is an oxidized porous Cu–Al alloy with a structure that is similar to Raney-type metals. The Raney process, patented by Murray Raney in 1925 and commercialized by W.R. Grace & Co., is one of the most successful routes for making porous metals. The problem is that this process requires extreme conditions that often restrict the final outcome at the nanometric scale. Here we opted for a different approach, applying a modified version of the ultrasound pore formation method that we have recently reported: high-power ultrasound. In a typical synthesis, Cu and Al beads are melted by using an electric arc. The resulting cake is then pulverized and sonicated in water. This gives a highly porous material containing pores predominantly at the micro-scale (see Figure 1a and 1b for a representative example; catalyst D).