(3-Aminopropyl)trimethoxysilane-Assisted Co-assembly to Monolithic Pd@SiO2/Al2O3/Al Catalysts for Low Concentration CH4 Combustion: Effect of Preparation Conditions

Herein, an affordable strategy was developed to form Pd@SiO2 nanostructure assembled onto monolithic AlOOH/Al nanoarrays from nano- to macro-scale by a one-step reaction process. (3-Aminopropyl)trimethoxysilane (APTMS) was employed as a dual-role reagent for the bidirectional bridging between Pd2+ and AlOOH/Al, as well as the formation of SiO2 matrix and mesopores. The effects of one-step organization conditions on the preparation process, catalyst structure, and catalytic performance were all studied. High hydroxyl contents in Al-based nanoarrays promoted the silanization reaction of APTMS deposition, resulting in a well-formed SiO2 shell and abundant mesopores during the thermal decomposition of APTMS. APTMS amount was not only related to SiO2 loading and encapsulation effect of the core–shell structure, but also affected Pd accessibility. Such proposed APTMS-assisted protocol for the in-situ organization of monolithic Pd@SiO2 catalysts can effectively prevent the growth and aggregation of Pd NPs, thereby favoring low-temperature activity and stability for CH4 combustion. Monolithic Pd@SiO2 catalysts supported on AlOOH/Al nanoarrays were successfully fabricated from nano- to macro-scale in one step for improved thermal stability of CH4 combustion. The cost-effective coupling agent (APTMS) acted as the bidirectional bridging between –NH2 of APTMS and Pd2+ through preferential chelation, as well as a silanization reaction between methoxy groups of APTMS and surface –OH groups on AlOOH nanoarrays to form Al–O–Si bonds.