Title: Mechanism by which Tungsten Oxide Promotes the Activity of Supported V ₂O ₅/TiO ₂ Catalysts for NO _X Abatement: Structural Effects Revealed by ⁵¹V MAS NMR Spectroscopy

Abstract

Growing concern for environmental pollutants coupled with an expansion of energy demand has promoted significant interest in technologies to abate contaminating species. Nitrogen oxides are particularly alarming due to their numerous detrimental impacts to the environment and public health, where selective catalytic reduction to inert N ₂ is an industrially-relevant mitigation technology. Herein, we provide unique, molecular-level insight on the structure and reactivity of V ₂O ₅(-WO ₃)/TiO ₂ catalysts employed at stationary facilities for NO _x removal. Detailed catalytic testing, spectroscopy (nuclear magnetic resonance, Raman, and electron paramagnetic resonance), and electronic structure-based predictions of ⁵¹V chemical shifts help clarify the promotional role of tungsten oxide and identify an active site requirement for SCR of NO _x. We show that progressive addition of vanadia to the catalyst surface increases the catalytic SCR performance and promotes the formation of larger vanadium domains, demonstrating the proportional relationship of SCR reaction rate to [VO _x loading]2 for supported V ₂O ₅/TiO ₂ catalysts with increasing surface vanadia coverage. Tungsten oxide incorporation enhances catalyst reactivity which is shown to stem not from electronic effects, but from changes to the vanadium structure as observed spectroscopically. The progressive addition of tungsten oxide to the catalyst surfacemore » also increases the catalytic performance and promotes the formation of larger vanadium domains, which are beneficial for catalytic turnover in a two-site model. Further, unique monomeric species are confidently ascribed to distorted tetrahedral and square pyramidal structures, resolving a long-standing uncertainty in literature assignments for the signals. These findings provide strong support for both the dual-site requirement for the SCR reaction and the important structural promotional effect that tungsten offers for mitigation of these harmful pollutants.« less

Authors:

Jaegers, Nicholas R.  ^[1];

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Lai, Jun-Kun ^[2]; He, Yang ^[3]; Walter, Eric ^[3]; Dixon, David A. ^[4]; Vasiliu, Monica ^[4]; Chen, Ying ^[3]; Wang, Chongmin ^[3]; Hu, Mary Y. ^[3]; Mueller, Karl T. ^[3]; Wachs, Israel E. ^[2]; Wang, Yong ^[1]; Hu, Jian Zhi  ^[3]

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+ Show Author Affiliations

1. Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Washington State Univ., Pullman, WA (United States)
2. Lehigh Univ., Bethlehem, PA (United States)
3. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
4. The Univ. of Alabama, Tuscaloosa, AL (United States)

Publication Date:

2019-07-08

Research Org.:

Pacific Northwest National Lab. (PNNL), Richland, WA (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)

OSTI Identifier:

1572978

Alternate Identifier(s):

OSTI ID: 1547078

Report Number(s):

PNNL-SA-141251
Journal ID: ISSN 1433-7851; ANIE

Grant/Contract Number:  

AC05-76RL01830; SC0012577; 66628

Resource Type:

Accepted Manuscript

Journal Name:

Angewandte Chemie (International Edition)

Additional Journal Information:

Journal Name: Angewandte Chemie (International Edition); Journal Volume: 58; Journal Issue: 36; Journal ID: ISSN 1433-7851

Publisher:

Wiley

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; heterogeneous catalysis; NMR spectroscopy; NOx; selective catalytic reduction (SCR); vanadium