Correlating the Structural Evolution of ZnO/Al2O3 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 Al2O3 catalysts with their structure and structural evolution. To this end, three model catalysts are investigated: (i) ZnO/Al2O3 prepared by atomic layer deposition (ALD) of ZnO onto gamma-Al2O3 followed by calcination at 700 degrees C, which yields a core-shell spinel zinc aluminate/gamma-Al2O3; (ii) zinc aluminate spinel nanoparticles (ZnxAlyO4 NPs) prepared via a hydrothermal method; and (iii) ZnO/SiO2 prepared by ALD of ZnO on SiO2. The catalysts are characterized by synchrotron X-ray powder diffraction (XRD), Zn K-edge X-ray absorption spectroscopy (XAS), and Al-27 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/SiO2. 50ZnO/Al2O3 gives 77% selectivity to propene at 9 mmol C3H6 g(cat)(-1) h(-1) space-time yield after 3 min of reaction at 600 degrees C. The ZnO/Al2O3 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 ZnxAlyO4 NPs due to coke deposition can be recovered by air regeneration.

Automated summary

In this study, the catalytic activity for propane dehydrogenation (PDH) of Zn-based Al2O3 catalysts was correlated with their structure and structural evolution. Four-tetrahedral Zn sites near Al sites in the zinc aluminate spinel phase were found to be more active and selective in PDH compared to the supported ZnO wurtzite phase. ZnO/Al2O3 catalyst exhibited 77% selectivity to propene, but experienced irreversible activity loss due to Zn depletion on the surface after repeated PDH and air-regeneration cycles.