Johnson Matthey Technol. Rev., 2022, 66, (1), 77
《Johnson Matthey Technology Review》实验室研究专题
In the Lab: Spotlight on Surface Characterisation Activities at Johnson Matthey
Johnson Matthey Technology Review features laboratory research
NON-PEER REVIEWED FEATURE
Received 23rd November 2021; Online 5th January 2022
Before joining Johnson Matthey, Tuğçe Eralp Erden was a Marie Curie PhD student at the University of Reading, UK, studying model chiral adsorption systems using synchrotron-based structural and spectroscopic techniques (1–5). After completing her PhD, she joined the advanced characterisation department at Johnson Matthey, Sonning Common, UK, where she is currently leading the surface spectroscopy team.
Johnson Matthey’s surface spectroscopy team focuses on providing essential information on the surface chemistry and composition of different materials for Johnson Matthey businesses and their customers. The team develops in situ, ex situ multi-technique surface analysis methods to deliver a more in-depth surface characterisation (6). Using laboratory-based X-ray photoelectron spectroscopy (XPS) as the main surface analysis technique, the team works on the applications of several complementary spectroscopic techniques such as ion scattering spectroscopy (ISS), reflection electron energy loss spectroscopy (REELS), ultraviolet photoelectron spectroscopy (UPS) and Raman.
The surface spectroscopy team is also involved in developing synchrotron-based near-ambient pressure (NAP)-XPS applications to study materials under reaction conditions. The team has been supporting fundamental surface science investigations and has sponsored several PhD projects that involved NAP-XPS characterisation of catalysts under reaction conditions. Two recent PhD projects with the University of Reading involved synchrotron-based NAP-XPS measurements to study supported platinum group metal (pgm) catalysts under methane oxidation reaction conditions in situ.
The first PhD project focused on investigating the chemical and compositional changes in alumina supported palladium catalysts with different particle sizes (4 nm to 10 nm) under reaction conditions similar to those used in the partial oxidation of methane to synthesis gas (syngas) (7). Surface adsorbates, palladium oxidation states and partial pressures of reactants and products were simultaneously tracked using mass spectrometry and NAP-XPS. NAP‐XPS data showed how the oxidation state of the palladium changes with increasing temperature (from Pd to PdO and back to Pd). NAP-XPS data analysis was further enhanced using mass spectrometry which showed an increase in carbon monoxide production over the Pd[II] oxide phase. In this study, a particle size effect was revealed for the catalysts demonstrating that methane conversion starts at lower temperatures with larger sized particles (Figure 1) (8).
For palladium catalysts on different supports such as alumina, silica and a mixture of alumina and silica, NAP-XPS showed that on all the supports studied PdO is the dominant oxidation state and is the active site for complete methane oxidation which occurs at 500–600 K. As the oxygen is consumed and the temperature increases to >650 K, PdO is found to reduce to PdOx, where 0 ≤ x < 1. Mass spectrometry showed a decrease in the partial pressures of complete methane oxidation products (carbon dioxide and water). Syngas formation (hydrogen and carbon monoxide), the product of partial methane oxidation, is dominant, suggesting reduced palladium is the active state for partial methane oxidation. The reactivity of alumina supported palladium materials is found to increase in the order: SiO2 < SiO2-Al2O3 < Al2O3 (Figure 2) (8).
Another collaborative PhD project (Johnson Matthey; Diamond Light Source, UK; and the University of Reading) involved studying the effect of pgm composition and reaction conditions (dry and wet) on the catalytic behaviour of a range of alumina supported monometallic palladium and bimetallic palladium-platinum nanocatalysts under methane oxidation conditions. NAP-XPS and in situ mass spectrometry were combined to correlate the product formation and the chemical state of the catalyst throughout the temperature ramps under methane and oxygen gas mixture at elevated temperatures under dry and wet conditions (Figure 3). NAP-XPS was used to study the chemical states of monometallic palladium and bimetallic palladium-platinum nanocatalysts, demonstrating that there is a clear link between platinum presence, palladium oxidation and catalyst activity under stoichiometric reaction conditions. Under oxygen-rich conditions this behaviour is found to be less clear, as all of the palladium tends to be oxidised, but there are still benefits to the addition of platinum in place of palladium for complete oxidation of methane (9).
T. Eralp, A. Ievins, A. Shavorskiy, S. J. Jenkins and G. Held, J. Am. Chem. Soc., 2012, 134, (23), 9615 LINK https://doi.org/10.1021/ja210499m
T. Eralp, A. Shavorskiy and G. Held, Surf. Sci., 2011, 605, (3–4), 468 LINK https://doi.org/10.1016/j.susc.2010.12.001
T. Eralp, A. Cornish, A. Shavorskiy and G. Held, Top. Catal., 2011, 54, (19–20), 1414 LINK https://doi.org/10.1007/s11244-011-9757-z
T. Eralp, A. Shavorskiy, Z. V. Zheleva, V. R. Dhanak and G. Held, Langmuir, 2010, 26, (13), 10918 LINK https://doi.org/10.1021/la1012796
T. Eralp, A. Shavorskiy, Z. V. Zheleva, G. Held, N. Kalashnyk, Y. Ning and T. R. Linderoth, Langmuir, 2010, 26, (24), 18841 LINK https://doi.org/10.1021/la1036772
W. W. McNeary, S. A. Tacey, G. D. Lahti, D. R. Conklin, Ki. A. Unocic, E. C. D. Tan, E. C. Wegener, T. E. Erden, S. Moulton, C. Gump, J. Burger, M. B. Griffin, C. A. Farberow, M. J. Watson, L. Tuxworth, K. M. Van Allsburg, A. A. Dameron, K. Buechler, and D. R. Vardon, ACS Catal., 2021, 11, (14), 8538 LINK https://doi.org/10.1021/acscatal.1c02101
R. Price, ‘Studying the Surface Chemistry of Methane Oxidation Catalysts with Near-Ambient Pressure X-Ray Photoelectron Spectroscopy’, PhD Thesis, School of Chemistry, University of Reading, Reading, UK, September, 2017, 169 pp LINK https://centaur.reading.ac.uk/78301/
R. Price, T. Eralp-Erden, E. Crumlin, S. Rani, S. Garcia, R. Smith, L. Deacon, C. Euaruksakul and G. Held, Top. Catal., 2016, 59, (5–7), 516 LINK https://doi.org/10.1007/s11244-015-0520-8
A. Large, J. Seymour, Wilson Q. Garzon, K. Roy, F. Venturini, D. C. Grinter, L. Artiglia, E. Brooke, M. B. de Gutierrez, A. Raj, K. R. J. Lovelock, R. A. Bennett, T. Eralp-Erden and G. Held, J. Phys. D: Appl. Phys., 2021, 54, (17), 174006 LINK https://doi.org/10.1088/1361-6463/abde67
Tuğçe Eralp Erden would like to thank the surface spectroscopy team (Riho Green, Charlotte Wise, Alex Oje, Matthew Forster), Johnson Matthey PhD students Alexander Large and Rachel Price, academic partners Professor Georg Held and Associate Professor Roger A. Bennett, Versox beamline team at Diamond Light Source, Johnson Matthey collaborators Agnes Raj, Luke Tuxworth and Mike Watson, the advanced characterisation department, and the director and technology managers of the Johnson Matthey Technology Centres.