Dynamic Structure and Subsurface Oxygen Formation of a Working Copper Catalyst under Methanol Steam Reforming Conditions: An in Situ Time-Resolved Spectroscopic Study

The dynamic behavior of a CuO/ZnO/Ga O catalyst under methanol steam reforming (MSR) reaction conditions promoted by a high dispersion of the copper nanoparticles and defect sites of a nonstoichiometric ZnGa O spinel phase has been observed, where structural changes taking place in the initial state of the reaction determine the final state of the catalyst in stationary reaction conditions. Mass spectrometry (MS) studies under transient conditions coupled to X-ray photoelectron spectroscopy (XPS) have shown copper oxidation to Cu in the initial state of the reaction (TOS = 4 min), followed by a fast reduction of the outer shell to Cu , while keeping dissolved oxygen species in the inner layers of the nanoparticle. The presence of this subsurface oxygen impairs a positive charge to the uppermost surface copper species, that is, Cu , which undoubtedly plays an important role on the MSR catalytic activity. The detection of these features, unperceived by conventional spectroscopic and catalytic studies, has only been possible by combining synchrotron NAP-XPS studies with transient studies performed in a low volume catalytic reactor connected to MS and linked with Raman and laboratory scale XPS studies.The research leading to these results has received funding from the European Union’s Seventh Framework Programme (FP/2007-2013) for the Fuel Cells and Hydrogen Joint Technology Initiative under Grant Agreement No. [303476]. Part of this work was financially supported by the following projects: (i) Project POCI-01-0145-FEDER-006939 (Laboratory for Process Engineering, Environment, Biotechnology and Energy – UID/EQU/00511/2013) funded by the European Regional Development Fund (ERDF), through COMPETE2020 - Programa Operacional Competitividade e Internacionalização (POCI) and by national funds, through FCT - Fundação para a Ciência e a Tecnologia; (ii) NORTE-01-0145-FEDER-000005 – LEPABE-2-ECO-INNOVATION, supported by North Portugal Regional Operational Programme (NORTE 2020), under the Portugal 2020 Partnership Agreement, through the European Regional Development Fund (ERDF); and (iii) the Spanish Government-MINECO through “Severo Ochoa” Excellence Programme (SEV-2016-0683). D.R. thanks European Research Council project SYNCATMATCH (671093). J.C. thanks the Spanish Government (MINECO) for a “Severo Ochoa” grant (BES-2015-075748). The NAP-XPS experiments were performed at the NAPP branch of the CIRCE beamline at the ALBA Synchrotron with the collaboration of ALBA staff