Copper/Titania Catalysts for the low temperature Water-Gas shift reaction; Effects of preparation methods on the catalyst activity and stability.
Abstract: 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 ... read moresupported 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%H2O-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
Thesis (M.S.)--Tufts University, 2015.
Submitted to the Dept. of Chemical and Biological Engineering.
Advisor: Maria Flytzani-Stephanopoulos.
Committee: Derek Mess, and Terry Haas.
Keyword: Chemical engineering.read less