Second Life Application of Automotive Catalysts: Hydrodynamic Cavitation Recovery and Photo Water Splitting

A hydrodynamic cavitation method was used to maximize the effect of destructuration of a honeycomb monolithic support of a spent Selective Catalyst Reduction (SCR) catalyst—V2O5-WO3/TiO2-type—for extracting crystalline titanium and tungsten oxides from the cordierite surface. A high relative inlet pressure of 40 MPa was applied to a divergent nozzle for obtaining high shear stresses of the submerged cavitating jets and intensive micro- and nano-jets and shock waves acting on the particle surface of the milled catalyst. Scanning Electron Microscopy (SEM) analysis indicated the compact morphology of the thin metal oxide layer at the surface of the cordierite support and the high content of Ti and W elements in the sample. Energy dispersive spectroscopy (EDAX) performed along with TEM investigations on different nano-zones from the sample established the elemental composition of WO3-TiO2 agglomerates separated after hydrodynamic cavitation processing and identified as independent nanocrystalline structures through Bright Field Transmission Electron Microscopy (BF-TEM) and High Resolution Transmission Electron Microscopy (HR-TEM) measurements. The tetragonal anatase phase of TiO2 and cubic phase of WO3 were established by both interplanar d spacing measurements and X-ray diffraction analysis. The photoelectrochemical results showed the possible second life application of automotive catalysts.