Catalytic urea hydrolysis by composite metal oxide catalyst towards efficient urea-based SCR process: performance evaluation and mechanism investigation

● Bimetallic oxide composite catalyst was designed for the urea-based SCR process.● Surface chemical state and typical microstructure of catalyst was determined.● Reaction route was improved based on intermediates and active site identification.● TiO2@Al2O3 presents an obvious promotion for urea hydrolysis.As a promising option to provide gaseous NH3 for SCR system, catalytic urea hydrolysis has aroused great attention, and improving surface area and activity of catalysis are the crucial issues to be solved for efficient urea hydrolysis. Therefore, a composite metal oxide （TiO2@Al2O3） catalyst was prepared by a simple hydrothermal method, with mesoporous alumina （γ-Al2O3） as substrate. The results verify the mesoporous structure and submicron cluster of TiO2@Al2O3, with exposed crystal faces of （101） and （400） for TiO2 and γ-Al2O3, respectively. The electronegativity difference of Ti4+ and Al3+ changes the charge distribution scheme around the interface, which provides abundant acid/base sites to boost the urea hydrolysis. Consequently, for an optimal proportioning with nano TiO2 content at 10 wt.%, the hydrolysis efficiency can reach up to 35.2 % at 100 °C in 2 h, increasing by 7.1 % than that of the blank experiment. 13C NMR spectrum measurements provide the impossible intermediate species during urea hydrolysis. Theoretical calculations are performed to clarify the efficient H2O decomposition at the interface of TiO2@Al2O3. The result offers a favorable technology for energy-efficiency urea hydrolysis.