Correlating the Structural Evolution of ZnO/Al 2 O 3 to Spinel Zinc Aluminate with its Catalytic Performance in Propane Dehydrogenation

We correlate the catalytic activity for propane dehydrogenation (PDH) of a series of Zn-based Al 2 O 3 catalysts with their structure and structural evolution. To this end, three model catalysts are investigated: (i) ZnO/Al 2 O 3 prepared by atomic layer deposition (ALD) of ZnO onto γ-Al 2 O 3 followed by calcination at 700 °C, which yields a core–shell spinel zinc aluminate/γ-Al 2 O 3; (ii) zinc aluminate spinel nanoparticles (Zn x Al y O 4 NPs) prepared via a hydrothermal method; and (iii) ZnO/SiO 2 prepared by ALD of ZnO on SiO 2 . The catalysts are characterized by synchrotron X-ray powder diffraction (XRD), Zn K-edge X-ray absorption spectroscopy (XAS), and 27 Al solid-state nuclear magnetic resonance (ssNMR). We identify tetrahedral Zn sites in close proximity to Al sites of a zinc aluminate spinel phase (Zn IV –O–Al IV/VI linkages) as more active and selective in PDH relative to the supported ZnO wurtzite phase (Zn IV –O– Zn IV linkages) in ZnO/SiO 2 . 50ZnO/Al 2 O 3 gives 77% selectivity to propene at 9 mmol C 3 H 6 g cat –1 h –1 space-time yield after 3 min of reaction at 600 °C. The ZnO/Al 2 O 3 catalyst shows an irreversible loss of activity over repeated PDH and air-regeneration cycles attributed to Zn depletion on the surface, while the activity loss of Zn x Al y O 4 NPs due to coke deposition can be recovered by air regeneration.