The relationships among the macroscopic compositional parameters of a Cu-exchanged SSZ-13 zeolite catalyst, the types and numbers of Cu active sites, and activity for the selective catalytic reduction (SCR) of NOx with NH3 are established through experimental interrogation and computational analysis of materials across the catalyst composition space. Density functional theory, stochastic models, and experimental characterizations demonstrate that within the synthesis protocols applied here and across Si:Al ratios, the volumetric density of six-membered-rings (6MR) containing two Al (2Al sites) is consistent with a random Al siting in the SSZ-13 lattice subject to Lowenstein’s rule. Further, exchanged CuII ions first populate these 2Al sites before populating remaining unpaired, or 1Al, sites as CuIIOH. These sites are distinguished and enumerated ex situ through vibrational and X-ray absorption spectroscopies (XAS) and chemical titrations. In situ and operando XAS follow Cu oxidation state and coordinatio...

Catalysis in a Cage: Condition-Dependent Speciation and Dynamics of Exchanged Cu Cations in SSZ-13 Zeolites

Operando X-ray absorption experiments and density functional theory (DFT) calculations are reported that elucidate the role of copper redox chemistry in the selective catalytic reduction (SCR) of NO over Cu-exchanged SSZ-13. Catalysts prepared to contain only isolated, exchanged CuII ions evidence both CuII and CuI ions under standard SCR conditions at 473 K. Reactant cutoff experiments show that NO and NH3 together are necessary for CuII reduction to CuI. DFT calculations show that NO-assisted NH3 dissociation is both energetically favorable and accounts for the observed CuII reduction. The calculations predict in situ generation of Bronsted sites proximal to CuI upon reduction, which we quantify in separate titration experiments. Both NO and O2 are necessary for oxidation of CuI to CuII, which DFT suggests to occur by a NO2 intermediate. Reaction of Cu-bound NO2 with proximal NH4+ completes the catalytic cycle. N2 is produced in both reduction and oxidation half-cycles.

Isolation of the Copper Redox Steps in the Standard Selective Catalytic Reduction on Cu‐SSZ‐13

A comparative electrochemical and quantum chemical calculation study of BTAH and BTAOH as copper corrosion inhibitors in near neutral chloride solution

Azoles and their derivatives are among the often used organic corrosion inhibitors for copper. For this reason, the adsorption of four azole molecules—imidazole, 1,2,3-triazole, tetrazole, and pent...

DFT Study of Interaction of Azoles with Cu(111) and Al(111) Surfaces: Role of Azole Nitrogen Atoms and Dipole–Dipole Interactions

Progress in corrosion science at atomic and nanometric scales

The adsorption of benzotriazole (BTAH) on Cu2O(111) was investigated with use of first-principles density functional theory calculations. Two possible adsorption structures were considered for both one-quarter and full adsorption coverage. We found that BTAH strongly chemisorbs (1.2−1.5 eV) onto Cu2O(111) by forming a chemical bond with a surface copper atom through nitrogen sp2 lone pairs, and a hydrogen bond with a surface oxygen atom through a C−H or N−H proton. The chemical interaction between the surface copper site and the molecule is the combined effect of a strong lone-pair → hybrid Cu-dz2spz σ-donation and a relatively weak dyz → 6π* back-donation. Vibration calculations were carried out to predict the BTAH−Cu2O stretching frequencies for both adsorption structures. The calculated stretching frequency (381 and 428 cm-1) could overlap with the BTAH benzene-ring torsion band. An estimate for the BTAH−Cu vibrational frequency (226 and 223.4 cm-1 for two adsorption modes, respectively) is in good agr...

Benzotriazole Adsorption on Cu2O(111) Surfaces: A First-Principles Study

The fundamental principle underlying the selective catalytic reduction (SCR) of NOx to N2 is the promotion of reactions of reductant with NOx over competing, and thermodynamically preferred, reactions with a large excess of O2. A similar competition between NOx and O2 exists in the noncatalytic, thermal reduction of NOx with NH3. In this work, density functional theory calculations are used to elucidate the origins of the remarkable selectivity in thermal deNOx. Thermal deNOx is initiated by the conversion of NH3 into the active reductant, NH2 radical. NH2 radical reacts with NO at rates typical of gas-phase radical reactions to produce a relatively strongly bound H2NNO adduct that readily rearranges and decomposes to N2 and H2O. In contrast, NH2 radical reacts exceedingly slowly with O2:  the H2N−OO adduct is weakly bound and more readily falls apart than reacts to products. The pronounced discrimination of NH2 against reaction with O2 is unusual behavior for a radical but can be understood through compa...

Molecular Origins of Selectivity in the Reduction of NOx by NH3

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Benzotriazole Adsorption on Cu2O(111) Surfaces: A First-Principles Study

Molecular Origins of Selectivity in the Reduction of NOx by NH3