2023 Abstracts.
181. X. Wu, M. Nazemi, S. Gupta, A. Chismar, K. Hong, H.P. Jacobs, W. Zhang,KaliRigby, T. Hedtke, Q. Wang, E. Stavitski, M.S.Wong, C. Muhich,and J.H. Kim. "Contrasting Capability of Single Atom Palladium for Thermocatalytic versus Electrocatalytic Nitrate Reduction Reaction"ACS Catalysis 3, 6804–6812 (2023) DOI: 10.1021/acscatal.3c01285
The occurrence of high concentrations of nitrate in various water resources is a significant environmental and human health threat, demanding effective removal technologies. Single atom alloys (SAAs) have emerged as a promising bimetallic material architecture in various thermocatalytic and electrocatalytic schemes including nitrate reduction reaction (NRR). This study suggests that there exists a stark contrast between thermocatalytic (T-NRR) and electrocatalytic (E-NRR) pathways that resulted in dramatic differences in SAA performances. Among Pd/Cu nanoalloys with varying Pd–Cu ratios from 1:100 to 100:1, Pd/Cu(1:100) SAA exhibited the greatest activity (TOFPd = 2 min–1) and highest N2 selectivity (94%) for E-NRR, while the same SAA performed poorly for T-NRR as compared to other nanoalloy counterparts. DFT calculations demonstrate that the improved performance and N2 selectivity of Pd/Cu(1:100) in E-NRR compared to T-NRR originate from the higher stability of NO3* in electrocatalysis and a lower N2 formation barrier than NH due to localized pH effects and the ability to extract protons from water. This study establishes the performance and mechanistic differences of SAA and nanoalloys for T-NRR versus E-NRR.
180. J. Levi, S. Guo, S. Kavadiya, Y. Luo, C. Lee, H.P. Jacobs, Z. Holman, M.S. Wong, S. Garcia-Segura, C. Zhou, B.E. Rittmann, P. Westerhoff "Comparing methods to deposit Pd-In catalysts on hydrogen-permeable hollow-fiber membranes for nitrate reduction" Water Research (2023) DOI: 10.1016/j.watres.2023.119877
Catalytic hydrogenation of nitrate in water has been studied primarily using nanoparticle slurries with constant hydrogen-gas (H2) bubbling. Such slurry reactors are impractical in full-scale water treatment applications because 1) unattached catalysts are difficult to be recycled/reused and 2) gas bubbling is inefficient for delivering H2. Membrane Catalyst-film Reactors (MCfR) resolve these limitations by depositing nanocatalysts on the exterior of gas-permeable hollow-fiber membranes that deliver H2 directly to the catalyst-film. The goal of this study was to compare the technical feasibility and benefits of various methods for attaching bimetallic palladium/indium (Pd/In) nanocatalysts for nitrate reduction in water, and subsequently select the most effective method. Four Pd/In deposition methods were evaluated for effectiveness in achieving durable nanocatalyst immobilization on the membranes and repeatable nitrate-reduction activity: (1) In-Situ MCfR-H2, (2) In-Situ Flask-Synthesis, (3) Ex-Situ Aerosol Impaction-Driven Assembly, and (4) Ex-Situ Electrostatic. Although all four deposition methods achieved catalyst-films that reduced nitrate in solution (≥ 1.1 min−1gPd−1), three deposition methods resulted in significant palladium loss (>29%) and an accompanying decline in nitrate reactivity over time. In contrast, the In-Situ MCfR-H2 deposition method had negligible Pd loss and remained active for nitrate reduction over multiple operational cycles. Therefore, In-Situ MCfR-H2 emerged as the superior deposition method and can be utilized to optimize catalyst attachment, nitrate-reduction, and N2 selectivity in future studies with more complex water matrices, longer treatment cycles, and larger reactors.
179. H.P. Jacobs, W.C. Elias, K.N. Heck, D.P. Dean, J.J. Dodson, W. Zhang, J.H. Arredondo, C.J. Breckner, K. Hong, C.R. Botello, L. Chen, S.G. Mueller, S.R. Alexander, J.T. Miller, and M.S. Wong "Impregnation of KOAc on PdAu/SiO2 causes Pd-acetate formation and metal restructuring" Journal of Materials Chemistry A (2023) DOI: 10.1039/D3TA00820G
Potassium-promoted, oxide-supported PdAu is catalytically active for the gas-phase acetoxylation of ethylene to form vinyl acetate monomer (VAM), in which the potassium improves long-term activity and VAM selectivity. The alkali metal is incorporated into the catalyst via wet impregnation of its salt solution, and it is generally assumed that this common catalyst preparation step has no effect on the catalyst structure. However, in this work, we report evidence to the contrary. We synthesized a silica-supported PdAu (PdAu/SiO2, 8 wt% Pd, 4 wt% Au) model catalyst containing Pd-rich PdAu alloy and pure Au phases. Impregnation with potassium acetate (KOAc) aqueous solution and subsequent drying did not cause XRD-detectible changes to the bimetal structure. However, DRIFTS indicated the presence of Pd3(OAc)6 species, which is correlated to up to 2% Pd loss after washing of the dried KOAc-promoted PdAu/SiO2. Carrying out the impregnation step with an AcOH-only solution and subsequent drying caused significant enlargement of the pure Au grain size and generated a smaller amount of Pd3(OAc)6. During co-impregnation of AcOH and KOAc, grain sizes were enlarged slightly, and substantial amounts of K2Pd2(OAc)6 and Pd3(OAc)6 were detected by DRIFTS and correlated to up to 32% Pd loss after washing. Synchrotron XAS analysis showed that approximately half the Pd atoms were oxidized, corroborating the presence of the Pd-acetate species. These results indicate wet-impregnation-induced metal leaching can occur and be substantial during catalyst preparation.
178. S. Yin, J.F. López, J.J.C. Solís, M.S. Wong and D. Villagrán "Enhanced adsorption of PFOA with nano MgAl2O4@CNTs: influence of pH and dosage, and environmental conditions" Journal of Hazardous Materials Advances 9, 100252 (2023) DOI: 10.1016/j.hazadv.2023.100252
Perfluorooctanoic acid (PFOA) has received extensive attention due to its widespread distribution in the environment and concerns of its exposure to human health. Nano-MgAl2O4 modified carbon nanotubes (CNTs) were synthesized, characterized, and used as nanoadsorbents to remove ppb (μg/L)-levels of PFOA from drinking water and brackish groundwater. Nano-MgAl2O4@CNTs composite materials were characterized by UV-Vis, FT-IR, DLS, p-XRD, BET, and SEM with EDX. The adsorption isotherms and kinetic studies were fitted to a Freundlich and to a pseudo-second-order models, respectively. Composite nano-MgAl2O4@CNTs remove over 99% of PFOA (100 ppb) from water in 3 hours, and completely (100%) in 3.5 hours. The optimal pH range is under mild alkaline conditions (pH = 7.5-9.0). Electrostatic and hydrophobic interactions drive the PFOA adsorption onto MgAl2O4@CNTs. The adsorption data of ground and drinking water samples indicated that nano-MgAl2O4@CNTs is an efficient nanoadsorbent for PFOA removal.