Abstract
The adaption of the sol–gel autocombustion method to the Cu/ZrO2 system opens new pathways for the specific optimisation of the activity, long-term stability and CO2 selectivity of methanol steam reforming (MSR) catalysts. Calcination of the same post-combustion precursor at 400 °C, 600 °C or 800 °C allows accessing Cu/ZrO2 interfaces of metallic Cu with either amorphous, tetragonal or monoclinic ZrO2, influencing the CO2 selectivity and the MSR activity distinctly different. While the CO2 selectivity is less affected, the impact of the post-combustion calcination temperature on the Cu and ZrO2 catalyst morphology is more pronounced. A porous and largely amorphous ZrO2 structure in the sample, characteristic for sol–gel autocombustion processes, is obtained at 400 °C. This directly translates into superior activity and long-term stability in MSR compared to Cu/tetragonal ZrO2 and Cu/monoclinic ZrO2 obtained by calcination at 600 °C and 800 °C. The morphology of the latter Cu/ZrO2 catalysts consists of much larger, agglomerated and non-porous crystalline particles. Based on aberration-corrected electron microscopy, we attribute the beneficial catalytic properties of the Cu/amorphous ZrO2 material partially to the enhanced sintering resistance of copper particles provided by the porous support morphology.
Highlights
Introduction200–300 1C as opposed to ethanol steam reforming with inherently reduced CO2 selectivity at temperatures above 400 1C).[1,2,3] Due to its high volumetric energy density, it is especially suitable for automotive applications, where the H2/CO2 reformate can be used in a polymer electrolyte membrane fuel cell (PEMFC).[1,4] For this application, the concentration of CO has to be kept in the low ppm regime, as even small traces of CO can deteriorate the performance of PEMFC electrodes.[5]
Kevin Ploner,a Parastoo Delir Kheyrollahi Nezhad,a Albert Gili, bc Franz Kamutzki,b Aleksander Gurlo,b Andrew Doran, d Pengfei Cao,e Marc Heggen,e Nicolas Kowitsch, f Marc Armbruster,f Maximilian Watschinger,a Bernhard Klotzera and Simon Penner *a
The obtained Zr precursor exhibits a similar tunability of its structure by application of different calcination treatments, whereas the temperature regions of stability are distinct from the copper-containing samples
Summary
200–300 1C as opposed to ethanol steam reforming with inherently reduced CO2 selectivity at temperatures above 400 1C).[1,2,3] Due to its high volumetric energy density, it is especially suitable for automotive applications, where the H2/CO2 reformate can be used in a polymer electrolyte membrane fuel cell (PEMFC).[1,4] For this application, the concentration of CO has to be kept in the low ppm regime, as even small traces of CO can deteriorate the performance of PEMFC electrodes.[5]. Various synthesis approaches for MSR catalysts are reported in literature, aiming at the optimisation of the activity, CO2 selectivity and long-term stability.[2] Among the most prominent ones are wet impregnation (Cu/ZrO2,19 Cu/Zn + Cu/Cr + CuZr on Al2O3,21 Cu/Al2O3 + Zn and Ce,[22] CeO2- + ZrO2-promoted Cu/ZnO on Al2O323) and co-precipitation (Cu/ZrO2,19 CuO/CeO2,24 ZrO2- and Al2O3-promoted Cu/ZnO,[25] Cu/CeO226), and other less commonly utilised methods like hydrothermal synthesis (Cu/ Zn/Al27), soft reactive grinding (Cu1.5Mn1.5O4 spinel28), oxalate gel co-precipitation (Cu/MnOx,[28] Cu/ZrO2,29 Cu/ZrO230), the polymer template sol–gel method (Cu/ZrO212) and urea nitrate combustion (Cu/CeO2,31 Cu/CeO2 doped with Sm, Zn, La, Zr, Mg, Gd, Y, Ca32) were employed Each of these syntheses offers certain advantages, but alternative methods satisfying all prerequisites of an ideal MSR catalyst are still to be developed. We correlate batch reactor studies, detailing the development of different trace products as a function of preMSR calcination temperature, with long-term stability tests in a flow reactor
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