Graphical Ammonia decomposition : Ni nanoparticles with a mean size of ∼2.3 nm anchored on Na-ZSM-5 nanocrystals were prepared as a catalyst to effectively crack ammonia for CO x -free H 2 production. Ammonia has been increasingly recognised as an effective hydrogen carrier to produce clean hydrogen free of CO x emissions. This study reports the development of Ni-based catalysts to efficiently crack ammonia into hydrogen and nitrogen. A series of catalysts with different Ni loadings supported on Na-ZSM-5 zeolite nanocrystals were prepared with the assistance of 1,10-phenanthroline ligand. The coordination of Ni and the ligand led to the formation of uniform Ni nanoparticles with a mean size of ∼2.3 nm. These small Ni nanoparticles of the catalyst enabled a high activity in ammonia decomposition evaluated using a fixed-bed reactor. Using the zeolite support in its pristine sodium form provided the catalyst with desired basicity. This promotes a strong metal-support interaction, leading the catalyst to have high stability. The catalyst with 5 wt% Ni loading exhibited a high TOF of 3.51 s −1 with no performance degradation at 650 °C for 50 h.
Catalytic oxidation is believed to be the most efficient method for indoor formaldehyde purification. Herein, we reported that the Pt/Na-ZSM-5 catalyst with low Pt loading (0.16 wt %) prepared by depositing Pt on Na+ ion-exchanged ZSM-5 could completely oxidize 300 ppm formaldehyde in 2.5 vol % H2O at 32 °C and maintain its activity during the 62 h-long stability test. Multiple characterizations revealed that the presence of Na species significantly enhanced formaldehyde adsorption ability and made Pt species tend to exist in the form of metal Pt through electron transfer from Na to Pt, which promoted the activation of oxygen and opened a new efficient formaldehyde oxidation pathway, namely, direct decomposition of formate. The synergistic effects resulted in the TOF of Pt(0.16)/Na-ZSM-5 being about nine times higher than that of Pt(0.50)/ZSM-5. Our study showed that utilizing an alkali metal to tune the surface acidity/basicity of the support and the state of the supported noble metal was a promising way to improve the intrinsic catalytic performance and reduce noble metal usage.
Yuchao Chai,Sihang Liu,Zhi-Jian Zhao,Jinlong Gong,Weili Dai,Guangjun Wu,Naijia Guan,Landong Li
Metal nanoparticles encapsulated in zeolite have been recently developed as a special type of catalyst that shows significant advantages in activity, shape-selectivity, and stability over conventional supported catalysts. The selectivity modulation of encapsulated nanoparticle catalysis by the zeolite microenvironment is theoretically possible but not addressed yet. Here, we report the in situ encapsulation of sub-nanometric palladium species within MFI-type zeolites, which exhibit high activity and good stability in the hydroconversion of furfural as a model reaction of biomass upgrading. Remarkably, different products, e.g., furan, furfural alcohol, and 1,5-pentanediol, from furfural hydroconversion can be obtained when silicalite-1, Na-ZSM-5, and H-ZSM-5 are employed as hosts of palladium nanoparticles, respectively. Density functional theory calculations and spectroscopy investigations reveal that both the adsorption of furfural and the activation of hydrogen are significantly affected by the zeolite microenvironment, leading to different reaction pathways. Our work presents an elegant example of catalytic selectivity modulation of encapsulated metal nanoparticles by tuning the zeolite microenvironment.
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