Preparation of Atomically-Dispersed Gold on Lanthanum Oxide as Active and Stable Catalysts for the Low-Temperature Water-Gas Shift Reaction.
hydrogen has been touted as the fuel of the future because, when combusted, it only
produces water, an environmentally innocuous by-product. The technology that would use
this H2 most efficiently is the fuel cell, which is capable of converting the chemical
energy stored in H2 into electrical energy that can be used to power daily life. Such a
device, though, requires very pur... read moree H2 as a fuel source without contaminating gases like
CO that poison the platinum catalysts on the anode of low temperature fuel cells. The
water-gas shift (WGS) reaction has been intensely studied as the most efficient way to
remove CO from H2 feeds to fuel cell systems. In such a design, a WGS reactor would
operate upstream of the fuel cell, at low temperature, to remove most or all of the CO
from the feed. Additional systems could also be implemented to further reduce the CO
content and remove other impurities (e.g. H2S). The current catalysts used in industrial
WGS reactors are Cu/ZnO/Al2O3. However, these catalysts are pyrophoric, require lengthy
activation procedures and show little thermal stability. Noble metal (Au, Pt, Pd, etc.)
catalysts have recently received significant attention as potential alternatives to the
industrial catalysts because they are non-pyrophoric and can be made more stable. In
this thesis, Au highly dispersed on La2O3 was investigated as a novel catalyst for the
WGS reaction. In particular, an anion adsorption technique was developed to deposit Au
onto the La2O3 surface in a manner that would favor a strong interaction between the Au
and the support. In this work, catalysts were prepared with four different techniques:
colloidal deposition, co-precipitation, deposition-precipitation, and anion adsorption.
These materials were characterized with electron microscopy (TEM), X-ray absorption
spectroscopy (XAS), BET surface area measurements, X-ray photoelectron spectroscopy
(XPS), and temperature programmed reduction (CO-TPR) studies. Additionally, Au/La2O3 was
studied under WGS reaction conditions in both product-free and full reformate gas
environments. Anion adsorption was found to produce the most active WGS catalyst
compared to other gold preparation techniques on lanthana. Additionally, it was observed
that high temperature treatments of 1% Au/La2O3 further activated these materials for
the WGS reaction. In an effort to improve our understanding of the importance of
reducible versus irreducible metal oxide supports in the WGS reaction, the surface
oxygen of the active gold catalysts was examined and quantified. It was discovered that
normalization of the reaction rates over Au/La2O3 by the amounts of active surface
oxygen were comparable to the similarly normalized rates of Au supported on reducible
metal oxides like CeO2 and FeOx.
Thesis (M.S.)--Tufts University, 2012.
Submitted to the Dept. of Chemical and Biological Engineering.
Advisor: Maria Flytzani-Stephanopoulos.
Committee: Howard Saltsburg, and George Kyriakou.
Keywords: Chemical engineering, and Chemistry.read less