Due to the uniform and stable pore structure, mesoporous silica has attracted increasing research attention as a catalyst support material. As a large family of mesoporous silica-supported materials, noble-metal nanoparticles supported on mesoporous silica catalysts have demonstrated desirable properties across a broad platform of reactions. In this review article, we first introduce systems of metal nanoparticles dispersed on mesoporous silica, and then, we focus on next generation systems, in which the noble metal is not supported on the mesoporous silica but rather entrapped/intercalated within the silica matrix, thus enhancing particle stability and in some cases, enhanced activity. Herein, research and future directions on both synthesizing hybrid noble-metal nanoparticles/mesoporous silica composite catalysts and their resultant properties will be discussed.
Nanostructured noble-metal catalysts
traditionally suffer from
sintering under high operating temperatures, leading to durability
issues and process limitations. The encapsulation of nanostructured
catalysts to prevent loss of activity through thermal sintering, while
maintaining accessibility of active sites, remains a great challenge
in the catalysis community. Here, we report a robust and regenerable
palladium-based catalyst, wherein palladium particles are intercalated
into the three-dimensional framework of SBA-15-type mesoporous silica.
The encapsulated Pd active sites remain catalytically active as demonstrated
in high-temperature/pressure phenol hydrodeoxygenation reactions.
The confinement of Pd particles in the walls of SBA-15 prevents particle
sintering at high temperatures. Moreover, a partially deactivated
catalyst containing intercalated particles is regenerated almost completely
even after several reaction cycles. In contrast, Pd particles, which
are not encapsulated within the SBA-15 framework, sinter and do not
recover prior activity after a regeneration procedure.
ZnO and Li‐doped ZnO photocatalysts were prepared by using a solvothermal method, aided by a supercritical drying technique. The structure and morphology of the photocatalysts were investigated by using SEM, X‐ray diffraction (XRD), UV/Vis and Raman spectroscopy. The photocatalytic activity and selectivity were investigated in the aqueous‐phase photodegradation of methylene blue and phenol as model reactions. Herein, it is reported for the first time that Li doping can lead to significant deactivation of the photocatalytic activity (i.e., decreased oxidization capability) of ZnO materials. The distribution of intermediate products (i.e., selectivity) was also significantly modified in the decomposition of phenol catalyzed by Li‐doped ZnO compared to that catalyzed by ZnO. Photoluminescence (PL) and soft X‐ray absorption spectroscopy (XAS) studies suggested that dopant‐induced surface‐defect states acted as electron–hole combination centers and changed the adsorbate/surface binding, thus causing the deactivation of photocatalytic activity and altering the photocatalytic selectivity in Li‐doped ZnO materials.
Gold nanoparticles physically trapped in the framework of alumina aerogel exhibit excellent thermal stability and catalytic activity at high temperature.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.