(762h) Effects of Surface Species and Dispersion in CeO2 Supported Transition Metal Oxide Catalysts for NO Reduction By CO Reaction

Effects
of Surface Species and Dispersion in CeO₂ Supported Transition Metal
Oxide Catalysts for NO Reduction by CO Reaction

Shuhao Zhang,¹Jaeha Lee,²
Do Heui Kim,²Taejin
Kim^1,*

¹ Department of
Materials Science and Chemical Engineering, Stony Brook University, Stony
Brook, NY, 11794, USA

² School
of Chemical and Biological Engineering, Institute of Chemical Processes, Seoul
National University, Seoul 08826, Republic of Korea

ABSTRACT:

Nitrogen oxides
(NO_x) are a main contributor to global air pollution ^[1].
In order to reduce the NO_x emission, there are several methods, such
as NH₃-SCR and NO reduction by CO, have been developed for the past
decades ^[2]. Currently, supported precious metals like Pt, Pd, and
Rh (PGMs) use for commercial catalytic converters to reduce NO_x
^[3]. Due to the high cost and scarcity of PGMs, however, alternative
catalysts such as transition metal oxides have received increasing attention ^[4].

In the current
study, series of CeO₂ supported CoO_x, NiO_x, or
FeO_x catalysts were prepared by incipient wetness impregnation method
for NO reduction by CO reaction. Catalytic activity and catalyst
physicochemical property were investigated by GC with TCD detector, XRD, BET, Raman
spectroscopy, and H₂-TPR. The specific surface area of the supported
catalysts decreased as the metal oxide loading increased. XRD results showed no
shifts regarding CeO₂ patterns, indicating that CeO₂ and
the transition metal oxides did not form solid solutions. Nanocrystalline Co₃O₄
(~690 cm^-1), NiO (~500 cm^-1), and Fe₂O₃
(~290 cm^-1) peaks were observed in the Raman spectra of 5 wt%, 6
wt%, and 10 wt% samples, respectively. The Raman results indicate 5-6 wt% CoO_x/CeO₂,
5-6 wt% NiO_x/CeO₂, and ~10% FeO_x/CeO₂
contains monolayer coverage. It was observed that both surface species and
dispersion are closely related to the catalytic activity in NO reduction by CO.
For example, for CoO_x/CeO₂ catalysts, monolayer and above
monolayer coverage catalysts showed 80~90% CO and NO conversion at >300^oC,
whereas sub-monolayer coverage catalysts had significantly low activity.
Similar results were also observed in FeO_x/CeO₂ and NiO_x/CeO₂
samples.

Figure. NO and CO conversions of CeO₂
supported transition metal oxide catalysts in NO reduction by CO reaction

ACKNOWLEDGMENT: We gratefully
acknowledge the financial support for this study from the Department of
Materials Science & Chemical Engineering at Stony Brook University.

[1]. K. Skalska, et al. Sci. Total Env., 408 (2010)
3976-3989, [2]. J.H. Kwak, et al., J. Catal., 287 (2012) 203-209, [3]. S. Roy,
et al., Applied Energy, 86 (2009) 2283-2297, [4]. X. Cheng, et al., Applied
Catal.B: Env. 239 (2018) 485–501