Modification of active metals with
metal oxide modifiers has attracted
considerable attention in heterogeneous catalysis due to their synergistic
effect. However, a controllable synthesis of highly reactive and stable
metal–metal oxide hybrid nanocatalysts is difficult. To solve
this problem, presynthesized IrM (M = Fe, Co, and Ni) bimetallic nanoparticles
were initially confined in the mesopores of SBA-15 and were then in situ transformed to Ir-MO
x
hybrids. The obtained Ir-MO
x
/SBA-15
nanocatalysts show superior activity and selectivity in the hydrogenation
of substituted nitroaromatics to corresponding aromatic amines compared
to Ir/SBA-15. Among these Ir-based catalysts, Ir-FeO
x
/SBA-15 exhibits the highest activity and selectivity and
has a wider substrate scope due to the interaction between Ir and
FeO
x
. Therefore, our research provides
a way to design reactive and stable hydrogenation catalysts.
Palladium nanoparticles supported on silica catalysts (Pd/SiO 2 ) were prepared by wet impregnation (WI), dry impregnation (DI), strong electrostatic adsorption (SEA), and charge-enhanced dry impregnation (CEDI) methods. The Pd/SiO 2 samples with highly dispersed and tight size-distributed palladium nanoparticles are obtained via SEA and CEDI methods based on strong electrostatic interactions between the dissolved metal precursor ([Pd(NH 3 ) 4 ] 2+ ) and positively charged SiO 2 support in an alkali-impregnating solution (initial pH = 12). The Pd/SiO 2 -SEA samples prepared by the SEA method usually showed higher palladium dispersions (>50%) than those prepared by CEDI (Pd dispersion = 32−45%). The surface loading (support surface area per liter of preparation solution), pH regulator (NaOH or NH 4 OH), Pd loading, and reduction temperature were shown to be key factors affecting the dispersion of palladium in the Pd/SiO 2 -SEA samples, as well as the leaching/dissolution of SiO 2 and palladium in the alkali solution. The Pd/SiO 2 -SEA samples prepared with proper SLs of 30,000−100,000 m 2 L −1 using NH 4 OH as the pH regulator exhibited not only very high Pd dispersions (64−97%) but also negligible losses of SiO 2 and Pd in the impregnating solution. The Pd/SiO 2 -SEA samples also exhibited better catalytic performance in methane combustion based on both the T 10 and T 50 temperatures and the intrinsic activities (mass-specific activity and/or turnover frequency (TOFs)). The TOFs generally decreased from 130 h −1 to 6.2 h −1 as Pd dispersion increased from 32% to 97% for the Pd/SiO 2 -SEA(NH 4 OH) catalysts. Moreover, the reaction activity of Pd/SiO 2 -SEA catalysts was significantly improved by increasing the fraction of Pd 0 in the range of 70−85%, indicating that this size-sensitive catalysis would be related to the redox properties of the supported Pd nanoparticles.
A series of NiP-x/Al2O3 catalysts containing different ratio of metallic nickel to nickel phosphides, prepared by varying Ni/P molar ratio of 4, 3, 2 through a co-impregnation method, were employed to investigate the synergistic effect of metallic nickel-nickel phosphides in dry methane reforming reaction. The Ni/Al2O3 catalyst indicates good activity along with severe carbon deposition. The presence of phosphorus increases nickel dispersion as well as the interaction between nickel and alumina support, which results in smaller nickel particles. The co-existence of metallic nickel and nickel phosphides species is confirmed at all the P contained catalysts. Due to the relative stronger CO2 dissociation ability, the NiP-x/Al2O3 catalysts indicate obvious higher resistance of carbon deposition. Furthermore, because of good balance between CH4 dissociation and CO2 dissociation, NiP-2/Al2O3 catalyst exhibits best resistance of carbon deposition, few carbon depositions were formed after 50 h of dry methane reforming.
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.