Low temperature NOx storage on zeolite supported Pd for low temperature diesel engine emission control

2018 Spring Symposium

L. Mantaroşie1, H.Y. Chen2, J. Collier1, D. Liu2, D. Duran-Martin1, V. Novak1, R. R. Rajaram1 and D. Thompsett1
1Johnson Matthey Technology Centre, Sonning Common, Reading, RG4 9NH, UK
2Johnson Matthey Inc., Emission Control Technology, Wayne, PA 19087, USA

Abstract – Recent legislation requirements have turned controlling NOx emissions into one of the biggest technical challenges facing car manufacturers [1]. At present, the main technologies available for this application are NO x storage and reduction (NSR) or urea based selective catalytic reduction (SCR) [2,3]. Both technologies can achieve high NO x reduction efficiencies once they reach their operating temperature (typically 200°C or higher). During cold start, when the exhaust temperature is below 200°C, both systems are less efficient at NOx removal.

To meet the NOx emission standards during the cold start (<200°C) a new concept has been introduced: passive NOx adsorbers (PNA) [4]. These are materials which store NOx (mainly as NO) at low temperatures and then thermally release the stored NOx once the downstream NOx reduction catalyst (NSR or SCR) reaches its operating temperature.

This contribution will report the remarkable ability of zeolite supported Pd to store NO with very high trapping efficiency at temperatures below 200°C and conditions that simulate real exhaust from diesel engines. The study will focus on the characterization of the Pd storage sites on zeolites compared to oxide supports and understanding unique nature of the active species in these materials. The properties of palladium supported on three different zeolites of various pore sizes (CHA, MFI and BETA) will be compared to classical oxidic supports (Al2O3 and CeO2).

Also, with the aim of providing insight into the behaviour of these materials during engine operation, the evolution of the NO storage sites under various gas feed compositions has been probed through combined “operando” IR and XAS experiments. The findings of these study will be discussed in relation to the realistic operation of the novel PNA technology.

References:
[1] L. Yang, V. Franco, A. Campestrini, J. German, P. Mock, ICCT report on NOX control technologies for Euro 6 Diesel passenger cars, 2015
[2] W.S. Epling, L.E. Campbell, A. Yezerets, N.W. Currier, J. E. Parks II, Catalysis Reviews, 163 (2004) 46.
[3] I. Nova, E. Tronconi (Eds.) Urea-SCR Technology for deNOx After Treatment of Diesel Exhausts, Springer New York, 2014.
[4] E. Melville, R.J. Brisley, O. Keane, P.R. Phillips, and E.H. Mountstevens, US patent 8, 105, 559, 2007

Influence of Confining Environment Polarity on Ethanol Dehydration Catalysis by Lewis Acid Zeolites

2018 Spring Symposium

Jason S. Bates and Rajamani Gounder, Charles D. Davidson School of Chemical Engineering, Purdue University, West Lafayette, IN

Abstract – The different reactivity of Lewis acid sites (M) in zeolite frameworks, when confined within non-polar (hydrophobic) or polar (hydrophilic) secondary environments, can arise from differences in competitive inhibition by solvents,1 solvent-mediated mechanisms,2 and extended solvent structures.3 Framework Lewis acid centers also adopt open ((HO)-M-(OSi≡)3) and closed (M-(OSi≡)4) configurations that show different reactivity for Baeyer-Villiger oxidation,4 glucose isomerization,3 and aldol condensation.5 Here, we interrogate the reactivity of Sn centers isolated within Beta zeolites using bimolecular ethanol dehydration to diethyl ether (404 K). Sn sites in open and closed configurations, quantified from IR spectra of adsorbed CD3CN before and after reaction, convert to structurally similar intermediates during ethanol dehydration catalysis (404 K) and revert to their initial configurations after regenerative oxidation treatments (21% O2, 803 K). Dehydration rates (404 K, 0.5–35 kPa C2H5OH, 0.1–50 kPa H2O) measured on ten low-defect (Sn-Beta-F) and high-defect (Sn-Beta-OH) zeolites were described by a rate equation derived from mechanisms identified by DFT calculations,6 and simplified using microkinetic modeling to identify kinetically-relevant pathways and intermediates. Polar hydroxyl defect groups located in confining environments preferentially stabilize reactive (ethanol-ethanol) and inhibitory (ethanol-water) dimeric intermediates over monomeric ethanol intermediates. As a result, equilibrium constants (404 K) for ethanol-water and ethanol-ethanol dimer formation are 3–4× higher on Sn-Beta-OH than on Sn-Beta-F, consistent with
insights from single-component and two-component adsorption measurements. Intrinsic dehydration rate constants (404 K) were identical among Sn-Beta-OH and Sn-Beta-F zeolites; thus, measured differences in dehydration turnover rates solely reflect differences in prevalent surface coverages of inhibitory and reactive dimeric intermediates at active Sn sites. The confinement of Lewis acidic binding sites within secondary environments of different defect density confers the ability to discriminate surface intermediates on the basis of polarity, providing a design strategy to accelerate turnover rates and suppress inhibition by water.

References:
[1] Conrad, S.; Wolf, P.; Müller, P.; Orsted, H., Hermans, I. ChemCatChem. 2017, 9, 175–182.
[2] Li, G.; Pidko, E.A.; Hensen, E.J.M. Catal. Sci. Technol. 2014, 4, 2241–2250.
[3] Harris, J.W.; Cordon, M.J.; Di Iorio, J.R.; Vega-Vila, J.C.; Ribeiro, F.H.; Gounder, R. J. Catal.
2016, 335, 141–154.
[4] Boronat, M.; Concepción, P.; Corma, A.; Renz, M.; Valencia, S. J. Catal. 2005, 234, 111–118.
[5] Lewis, J.D.; Ha, M.; Luo, H.; Faucher, A.; Michaelis, V.K.; Román-Leshkov, Y. ACS Catal. 2018,
3076–3086.
[6] Bukowski, B.C.; Bates, J.S.; Gounder, R.; Greeley, J. J. Catal. 2018, under review.

Fabrication of Nano-Structured Catalyst Supports by ALD

2018 Spring Symposium

Raymond J. GorteChemical & Biomolecular Engineering, University of Pennsylvania, Philadelphia, PA

Abstract – Interactions between a transition-metal catalyst and its support can strongly alter the stability and activity of the catalyst. Important examples include support effects with ceria and the so-called “Intelligent Catalysts” in which the metal can be redispersed by reversible ex-solution from a perovskite lattice. However, the surface areas of these functional supports are often too low or unstable; and, in the case of perovskites, the length scales for ingress and egress may be too long to take advantage of the effect. We are addressing these issues by depositing very thin films of various functional oxides, ~0.5 to 2 nm thick, onto high-surface-area supports, including Al2O3 and MgAl2O4 , by Atomic Layer Deposition. We have demonstrated that a wide range of oxides can be deposited as dense, uniform, conformal films on various supports. The films exhibit surprisingly good thermal stability and provide catalytic properties similar to that observed with bulk oxides, but with higher surface areas.

Spectroscopic Technique Development for Understanding Solvent Effects in Liquid Phase Reactions

Meeting Program – April 2018

Nicholas Gould – Student Speaker

Advisor: Bingjun Xu
Department of Chemical and Biomolecular Engineering
University of Delaware
 

Abstract – Biomass conversion reactions are frequently conducted in a solvent, due to the highly oxygenated nature of the feedstock.1,2 Thus, heterogeneous catalytic active sites exist at a solid-liquid interface, where the solvent can modify surface and adsorbate energetics. Even when the solvent does not play a direct role in the reaction mechanism, it can stabilize or destabilize adsorbates, intermediates, and transition states, often leading to markedly different rates and selectivities between solvent choices.3–5 However, solvent effects are poorly understood because catalyst characterization techniques, such as probe molecule adsorption in FTIR, are most often conducted under vacuum or in vapor phase.6,7 Further, most studies on solvent effects focus on screening solvents via catalytic activity testing, where multiple factors that can influence reactivity exist simultaneously: competitive adsorption, stabilization of reactants and transition states, and phase equilibria differences. Thus, there is currently a need for experimental techniques capable of extracting fundamental thermodynamic properties of solvents in simple systems, with the end goal of decoupling the effects of solvent in catalytic activity tests.8

Attenuated total reflection (ATR) fourier transform infrared spectroscopy (FTIR) was used to characterize zeolites with probe molecules in the presence of solvent. The ATR-FTIR was further developed into a quantitative technique, with a procedure for determining extinction coefficients for adsorbed pyridine on zeolites in the presence of solvent.9 This allowed for quantitative comparisons of the effect of solvent on probe molecule uptake and protonation in zeolite pores. Ongoing applications of the ATR-FTIR cell include adsorption isotherms, diffusion measurements, and temperature programmed desorption (TPD) in porous materials in liquid phase. Further, the effect of solvent on charge stabilization in zeolite pores was studied using a homemade TPD set up under back pressurized, flowing solvent. Preliminary pyridine desorption temperatures from an H/ZSM-5 sample reveal that the ability of a solvent to stabilize pyridinium ions decreases in the order: water > acetonitrile > alkane ≈ vacuum.

References:

  1. G. W. Huber, S. Iborra and A. Corma, Chem. Rev., 2006, 106, 4044–4098.
  2. D. M. Alonso, S. G. Wettstein and J. A. Dumesic, Green Chem., 2013, 15, 584–595.
  3. M. A. Mellmer, C. Sener, J. M. R. Gallo, J. S. Luterbacher, D. M. Alonso and J. A. Dumesic, Angew. Chemie – Int. Ed., 2014, 53, 11872–11875.
  4. P. J. Dyson and P. G. Jessop, Catal. Sci. Technol., 2016, 6, 3302–3316.
  5. J. F. Haw, T. Xu, J. B. Nicholas and P. W. Goguen, Nature, 1997, 389, 832–835.
  6. F. Zaera, Chem. Rev., 2012, 112, 2920–2986.
  7. H. Shi, J. Lercher and X.-Y. Yu, Catal. Sci. Technol., 2015, 5, 3035–3060.
  8. N. Gould and B. Xu, Chem. Sci., 2018, 9, 281–287.
  9. N. S. Gould and B. Xu, J. Catal., 2017, accepted.

Novel catalyst architectures for automotive emission control

Meeting Program – April 2018

Johannes W. Schwank
Johannes W. Schwank
James and Judith Street Professor of Chemical Engineering
Department of Chemical Engineering
University of Michigan
Ann Arbor, Michigan

 

Abstract – Two novel automotive emission control catalyst architectures will be discussed, namely core@shell structures for low-temperature three-way catalysts, and cobalt-based nanorod structures for diesel oxidation catalysts that minimize expensive platinum-group metals.

Encapsulating an active metal core such as palladium in a porous oxide shell material can lead to improved catalytic activity, selectivity, and thermal stability compared to conventional supported catalysts. Maintaining high dispersion of palladium is critical for Pd-based automotive emission control catalysts, which suffer from deactivation due to sintering at high temperatures (≥ 800 °C). Here, we report direct evidence that Pd nanoparticles (~4 nm) can redisperse into small nanoclusters after aging at 800 °C, where severe Pd sintering would be expected on supported Pd catalysts. The Pd redispersion was confirmed by in situ, as well as ex situ, high-resolution transmission electron microscopy, and is manifested by the decreased CO light-off temperature. These novel core@shell structures exhibited remarkable thermal stability, maintaining the particle size and pore structure at very high temperatures (800-900 °C), close to those one may encounter in three-way automotive emission control applications.

Co3O4-In2O3 binary oxide nanorods offer a pathway for low-cost, efficient diesel emission control systems. The catalytic tests results showed that the catalysts were highly active for CO and propene oxidation, with low temperature light-off curves. The activity and stability of these cobalt oxide catalysts were comparable to platinum-based catalysts, indicating that they could be a potential substitute for platinum-based catalysts for diesel emission control.

Biography – Johannes Schwank holds a Ph. D. degree in Physical Chemistry from Innsbruck University in Austria. He joined the faculty at the University of Michigan in 1980 where he rose through the ranks and became Full Professor of Chemical Engineering in 1990. He served as Chairman of the Chemical Engineering Department from 1990 – 1995, as Interim Director of the University of Michigan Energy Institute 2011/2012, and as Director of EMAL (Electron Microbeam Analysis Laboratory), a campus-wide user facility 2013-2015. He is the holder of the James and Judith Street Chair in Chemical Engineering and the Director of REFRESCH, an interdisciplinary project that deals with food, energy, and water security in resource–constrained environments.

He serves on multiple editorial boards and industrial and academic advisory boards. He has co-founded a successful start-up company, Akervall Technologies. He is the author of more than 200 refereed publications, and holds 15 patents. His research group is working on a wide range of topics, including nanostructured materials for catalysis, energy storage, and gas sensing applications; synthetic fuels; biomass conversion; hydrogen production; solid oxide fuel cells; automotive emission control catalysts; photocatalysis; and novel catalyst synthesis and characterization methods.

Morphological Instability in Topologically Complex, Three-Dimensional Electrocatalytic Nanostructures

Meeting Program – March 2018

Yawei Li – Student Speaker

Advisor: Joshua Snyder
Department of Chemical and Biological Engineering
Drexel University, Philadelphia, Pennsylvania 19104
 

Abstract – Dealloying has shown increasing utility in the field of electrocatalysis as a tool for the synthesis and development of nanoporous materials possessing high surface-to-volume ratios with controlled morphology and compositional gradient (core-shell structure). After electrochemical dealloying, the open, bicontinuous, three-dimensional nanoporous nanoparticle electrocatalysts exhibit dramatically enhanced electrocatalytic properties.

In the development of efficient electrocatalysts for oxygen reduction reaction (ORR), durability is too often ignored in the pursuit of higher activities. For 3-dimensional, nanoporous materials, in addition to the standard mechanisms of electrocatalyst degradation including Pt dissolution/Ostwald ripening and coalescence/aggregation, new modes of morphological and compositional evolution must be considered. Here we use a combination of in-situ and ex-situ experimental techniques to develop insight into the structural and compositional evolution of nanoporous PtNi nanoparticles (np-NiPt) formed through the dealloying of Pt 20 Ni 80 precursor nanoparticles. We demonstrate that surface-diffusion facilitated coarsening, driven by the tendency to reduce the overall surface free energy of the system, is the dominant mechanism of electrochemical active surface area (ECSA) loss, consequently resulting in a decrease in activity.

With a better understanding of the interplay between nanoporous structure coarsening and transition metal loss, we have developed strategy to mitigate coarsening and improve operational catalyst stability by impeding step edge movement through the use of foreign adsorbates on the
surface. We show that partial monolayer decoration of np-NiPt with Ir, possessing a significantly lower rate of surface diffusion than Pt, acts to pin step edges and results in significant enhancement in catalyst durability as measured by ECSA and ORR activity retention. With this strategy we will show how more detailed insight into the atomic processes that govern electrocatalytic material instability can begin to break the inverse correlation between activity and durability.

Synthesis of Nanosized Zeolites For Different Catalytic Applications

Meeting Program – March 2018

Manuel Moliner
Manuel Moliner
Tenured Scientist, Instituto de Tecnología Química (UPV-CSIC)
Universidad Politécnica de Valencia,
Consejo Superior de Investigaciones Científicas

 

Abstract – On the one hand, the preparation of different zeolites, i.e. Beta and ZSM-5, in their nanosized forms with controlled Si/Al molar ratios (~15-30), high solid yields (above 90%), and homogeneous crystal sizes (~10-25 nm), has been achieved by using simple bifunctional alkyl-substituted mono-cationic cyclic ammonium cations as OSDA molecules [1]. These OSDAs combine a cyclic part and a short alkyl-chain group (preferentially C4) and, depending on the size and nature of the cyclic fragment, the crystallization of different zeolites can be controlled. The catalytic properties of the achieved nanosized zeolitic materials have been evaluated for the methanol-to-olefins and olefin oligomerization reactions [1].
On the other hand, the efficient synthesis of the small-pore CHA and AEI zeolites with nanosized crystals (20—50 nm) has also been obtained following zeolite-to-zeolite transformation procedures, where high-silica FAU materials have been used as silicon and aluminum precursors [2]. The nanosized small pore zeolites have been evaluated for the methanol-to-olefin reaction, observing that their catalyst lifetimes are remarkably longer than the catalyst lifetimes observed for conventional small pore zeolites. In addition, the selectivity towards different light olefins, i.e. propylene and/or ethylene, can be maximized depending on the crystalline structure of the nanosized zeolites.

References:

  1. (a) E.M. Gallego et al., Chem. Sci., 2017, 8, 8138.; (b) M.R. Díaz-Rey et al., ACS Catal., 2017, 7, 6170.
  2. N. Martín et al., Chem. Commun., 2016, 52, 6072.

Biography – Manuel Moliner obtained his B.S. degree in Chemical Engineering at the University of Valencia (Spain) in 2003, and completed his Ph.D. at the Polytechnic University of Valencia (UPV, Spain), in Chemistry, under the guidance of Prof. Avelino Corma in 2008. Afterward, he completed a two-year postdoc (2008-2010) with Prof. Mark Davis at the California Institute of Technology (Caltech, USA).
He is a Tenured Scientist of the Spanish National Research Council (CSIC) since 2014, where his research lies at the interface of heterogeneous catalysis and materials design.
Manuel Moliner has published 70 papers in international journals, and is co-inventor of 24 international patents (14 transferred to industry). He has received different national and international awards, as the “EFCATS Thesis Award” to the best Ph.D. Thesis in Europe in 2007-2009, the “TR-35 Spain 2011” awarded by MIT to young talents in Spain under-35, or the “FISOCAT 2014” to young scientists under 40 in Latin America.