(744g) Aldehyde Water Shift Reaction: Comparative Investigation of Supported Metal Catalysts

Wen, W. C. - Presenter, University of Michigan
Thompson, L. T., University of Michigan

There has been significant interest in the use of H2O
as a reactant for biomass conversion given its high concentration in typical
feed streams.
reforming and 5-hydroxymethylfurfural oxidation are two important examples.[1], [2] The
aim of research described in this paper was to investigate the use of H2O as a terminal oxidant for the partial oxidation of
aldehydes. The aldehyde water shift (AWS) reaction oxidizes the aldehyde
and produces H2 (Equation 1).

+ H2 (Eq. 1)

Prior investigations of the
AWS reaction have focused on homogeneous catalysts.[3] The commercial
implementation of these types of catalysts can be cost-prohibitive. To our
knowledge, no heterogeneous catalyst has been reported for this reaction. We explored
the use of Mo2C-, CeO2-, and Al2O3-supported
metals (Cu, Pt, Au), the design of which was inspired by that for highly active water
gas shift (WGS) catalysts. In particular, the most active heterogeneous WGS
catalysts are bifunctional and possess distinct sites for H2O dissociation
and CO oxidation.[4] The target metal
loadings were equivalent to 0.1 monolayer. The catalysts were loaded into a
quartz flow-through reactor and the reactions were then carried out at 200-280oC.

The AWS activities (Figure.
1) and product distributions (Figure. 2) were strong functions of the support. The
observed AWS activities and activation energies suggest that the rate-limiting
step, which is believed to be H2O dissociation, occurred on the support surface. Among
all the catalysts studied, the Mo2C-supported catalysts possessed the highest AWS activities, with activities at least 5 times
higher than those for the other materials. For the Mo2C-supported catalysts,
the admetal did not significantly affect the activity. The Cu/CeO2
showed the highest AWS activity among the CeO2-supported materials. Like Mo2C, CeO2 is
active for H2O dissociation. The
high activity of the Cu/CeO2 catalyst clearly illustrates the
importance of Cu particles for
this material. In addition
to the AWS reaction, the major side
reactions were the Cannizzaro reaction, which produces ethanol and acetic acid,
and aldol condensation, which forms crotonaldehyde. The Mo2C-supported
catalysts and Cu/CeO2 were more than 60% selective
to the AWS reaction. Our results suggest that the cooperation between the sites
for H2O dissociation and aldehyde oxidation may have contributed
to the high AWS activities and selectivities. In contrast, the other
CeO2- and Al2O3-supported catalysts produced primarily
crotonaldehyde via the aldol condensation
reaction, which appeared to be catalyzed by weak acid sites. These and other results will be presented
in the paper.



[1]      Davda, R. R.; Shabaker,
J. W.; Huber, G. W.; Cortright, R. D.; Dumesic, J. A. Appl. Catal. B
2005, 56, 171-186

[2]      Zhang, Z.; Deng, K.
ACS Catal. 2015, 5, 6529-6544

[3]      Brewster, T. P.; Goldberg,
J. M.; Tran, J. C.; Heinekey, D. M.; Goldberg, K. I. ACS Catal. 2016,
6, 6302-6305

[4]      Schweitzer, N. M.; Schaidle,
J. A. ; Ezekoye, O. K.; Pan, X. ; Linic, S.; Thompson, L. T. J. Am. Chem.
2011, 133, 2378-2381