Size-dependent catalytic performance of CuO on γ-Al2O3: NO reduction versus NH3 oxidation

Journal Article · Fri May 25 04:00:00 EDT 2012 · ACS Catalysis

DOI:https://doi.org/10.1021/cs3002463· OSTI ID:1047375

Kwak, Ja Hun; Tonkyn, Russell G; Tran, Diana N; Mei, Donghai; Cho, Sung June; Kovarik, Libor; Lee, Jong H; Peden, Charles HF; Szanyi, Janos

Catalytic reaction pathways of NH{sub 3} on CuO/{gamma}-Al{sub 2}O{sub 3} catalysts during NH{sub 3} SCR reactions were investigated under oxygen-rich conditions. On 10 wt % CuO/{gamma}-Al{sub 2}O{sub 3}, NH{sub 3} reacted with oxygen to produce NO{sub x}. In contrast, on the 0.5 wt % CuO/{gamma}-Al{sub 2}O{sub 3} catalyst NH{sub 3} reacted primarily with NO to form N{sub 2} with conversion efficiency of {approx}80% at 450 C. H{sub 2}-TPR results show that Cu species present in 10 wt % CuO/{gamma}-Al{sub 2}O{sub 3} can be easily reduced at {approx}160 C, which suggests the formation of large CuO clusters on the alumina surface. On the other hand, the TPR spectrum obtained from the 0.5 wt % CuO/{gamma}-Al{sub 2}O{sub 3} catalyst does not show any measurable H{sub 2} consumption up to 700 C, which suggests the presence of non-reducible isolated Cu species in this catalyst. STEM images collected from 10 wt % CuO/{gamma}-Al{sub 2}O{sub 3} show nano-sized CuO clusters, while no evidence of cluster formation is seen in the images recorded from the 0.5 wt % CuO/{gamma}-Al{sub 2}O{sub 3} sample, due to the intrinsic limitation of low Z contrast between highly dispersed Cu (atomic weight = 63.5) species and the alumina support (atomic weight of Al = 27). EXAFS data indicates the presence of Cu-Cu (Al) second shell at 0.35 nm only in the 10% CuO/{gamma}-Al{sub 2}O{sub 3} catalyst, and an estimated coordination number of {approx}1.7. The XANES and EXAFS results suggest the formation of relatively highly dispersed Cu oxide nanoclusters even at 10 wt % Cu loading. However, FT-IR spectra collected after CO adsorption on the CuO/{gamma}-Al{sub 2}O{sub 3} catalysts demonstrate the existence of different Cu species at Cu loadings of 0.5 and 10 wt %. Density functional theory (DFT) results show that supported CuO clusters, represented by a two-dimensional (2D) CuO monolayer, can effectively dissociate adsorbed NO and O2 to produce atomic oxygen species. These reactive atomic oxygen species then react with NH{sub 3} to produce NO{sub x}. However, the non-reducible, isolated Cu species, modeled by {gamma}-Al{sub 2}O{sub 3}-supported monomeric CuO, shows relatively weaker interactions with both NO and O{sub 2}. Most importantly, our calculations suggest that the dissociations of NO and O{sub 2} are energetically unlikely on this latter catalyst. Therefore, molecularly adsorbed NO can only react with NH{sub 3} to produce N{sub 2} on the low (0.5 wt %) CuO-loaded catalyst.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1047375
• Report Number(s): PNNL-SA-81197; 35404; VT0401000
• Journal Information: ACS Catalysis, Journal Name: ACS Catalysis Journal Issue: 7 Vol. 2
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
ADSORPTION
Ammonia
CATALYSTS
CONVERSION
COORDINATION NUMBER
Copper oxide
DATA
DENSITY
Density functional theory
EFFICIENCY
Environmental Molecular Sciences Laboratory
FUNCTIONALS
IMAGES
INTERACTIONS
LOADING
Morphological effects
Nitric oxides
OXIDATION
OXIDES
OXYGEN
PERFORMANCE
SELECTIVE CATALYTIC REDUCTION
SPECTRA
Selective catalytic reduction
WEIGHT
γ-alumina