Copper/Titania Catalysts for the low-temperature Water-gas shift reaction: Effects of preparation methods on the catalyst activity and stability.

摘要

The water gas shift reaction (WGS) is a necessary step for many hydrogen streams produced from carbon-based sources. Fisher Tropsch synthesis, fuel processing, ammonia synthesis, methanol formation, and many more chemical processes involve the WGS reaction to effectively remove or change the level of carbon monoxide and increase the hydrogen amount. For over nearly a century copper supported on zinc oxide has been the standard industrial catalyst for the low-temperature WGS reaction. There have been many improvements made in terms of stabilizing the catalyst and venture into more expensive noble metals has been successfully done along with use of various supports. Understanding the catalyst mechanism and the role of the support is still being debated today.;Work done for this thesis focused on copper, and how the roles of the support come into effect for the WGS reaction. Titania was used as a support and three main catalyst preparations were made: deposition precipitation, UV-assisted deposition precipitation, and solution gelation. Each preparation was done to test changes in catalyst composition effect on activity, light off temperature, and eventually the most successful were compared for stability and kinetics. Parametric study of the Sol-gel catalyst was done by changing the hydration route, calcination temperature, and copper loading. Product- free WGS conditions were tested for 3%H2O-10%CO-He, and 5%H 2O-10%CO-He. These catalysts were compared mainly by XRD, XPS, WGS-TPSR and ICP with the most active catalyst having the stability, kinetics (apparent activation energy), and leaching done. Leaching was done to remove large copper particles and see the catalytic effect of the more strongly bound copper species.;From characterization and activity measurements, conclusions about the support effect and preparation were made. Small particle, doped titania is expected to have more oxygen vacancies and this increased as loading and temperature increased resulting in a more active supported copper catalyst. However, a lower loading with less apparent copper to titania ratio on the surface (DP prepared catalyst) proved to be more active in both conversion and light off temperatures. This less defect-containing supported catalyst had a lesser extent of copper particle growth, however, which may chiefly explain its higher activity. Copper nanoclusters not associated with a support have been known to catalyze the WGS reaction to a lesser extent. Apparent activation energies for the 5%at Cu DP, and 30%at Cu Sol-Gel were 46.8+/-1.6 and 42.6+/-1.2 kJ/mol, respectively, which fall in the range for copper ceria catalysts from the literature. Analogy to ceria supported copper catalyst showed similar patterns in the effect of doping and importance of defects ion the support. The sol-gel doped with copper may prove an interesting catalyst to further develop with proper treatment to control the surface amount of copper or another WGS catalyst metal, as such the small titania particle (5 nm) support is ideal for defect formation.