Morphologically tailored facet dependent silver nanoparticles supported α-Al₂O₃ catalysts for chemoselective reduction of aromatic nitro compounds

AbstractThe nanoparticles surface area, intrinsic sites, exposed microcrystal shapes and lattice planes are some of the key factors in nanocatalysis. The influence of nanoparticles shape dependent had been profound effect on its catalytic activity. This study is focused on the synthesis of morphologically shape-controlled silver (Ag) nanoparticles supported on α-Al₂O₃ catalysts were performed. The correlation of Ag NPs with varied facets and lattice planes on the catalytic activities in chemoselective reduction of nitro compounds was investigated. Engineering the silver nanoparticles with different shapes and facets i.e., nanocubes (AgNCs), nanowires (AgNWs) and nano spheres (AgNSPs) were synthesized by using modified polyol method. It is demonstrated that there is a significant difference in their activities with respect to the shape and nanocrystal facets. The evolution of nanoshapes and the structural properties of Ag nanoparticles were analysed by SEM, TEM, HR-TEM and P-XRD techniques. From XRD, Ag nanocubes exhibited high percentage of low index (1 0 0) facets which are favourable active centers than (1 1 1) plane in nitro reduction. We observed that the silver nanocubes selectively exposed (1 0 0) facets, which are highly favorable for the enhanced catalytic activity in nitro reduction. The reaction rate of nitro phenol to amino phenol over different Ag nanoshapes are 35.01×10−3min−1(AgNCs/Al₂O₃), 8.28×10−3min−1(AgNWs/Al₂O₃), 0.65×10−3 min−1(AgNSPs/Al₂O₃), respectively. The calculated thermodynamic parameters of the Ea values 23.6, 28.6 and 29.4 for the AgNC, AgNWs and AgNSP respectively.Abstract The nanoparticles surface area, intrinsic sites, exposed microcrystal shapes and lattice planes are some of the key factors in nanocatalysis. The influence of nanoparticles shape dependent had been profound effect on its catalytic activity. This study is focused on the synthesis of morphologically shape-controlled silver (Ag) nanoparticles supported on α-Al₂O₃ catalysts were performed. The correlation of Ag NPs with varied facets and lattice planes on the catalytic activities in chemoselective reduction of nitro compounds was investigated. Engineering the silver nanoparticles with different shapes and facets i.e., nanocubes (AgNCs), nanowires (AgNWs) and nano spheres (AgNSPs) were synthesized by using modified polyol method. It is demonstrated that there is a significant difference in their activities with respect to the shape and nanocrystal facets. The evolution of nanoshapes and the structural properties of Ag nanoparticles were analysed by SEM, TEM, HR-TEM and P-XRD techniques. From XRD, Ag nanocubes exhibited high percentage of low index (1 0 0) facets which are favourable active centers than (1 1 1) plane in nitro reduction. We observed that the silver nanocubes selectively exposed (1 0 0) facets, which are highly favorable for the enhanced catalytic activity in nitro reduction. The reaction rate of nitro phenol to amino phenol over different Ag nanoshapes are 35.01×10−3min−1(AgNCs/Al₂O₃), 8.28×10−3min−1(AgNWs/Al₂O₃), 0.65×10−3 min−1(AgNSPs/Al₂O₃), respectively. The calculated thermodynamic parameters of the Ea values 23.6, 28.6 and 29.4 for the AgNC, AgNWs and AgNSP respectively

Insight into the role of metal support interface through the synergistic effect between Ag and α-Bi2Mo3O12 support for the selective oxidation of propylene to acrolein

Abstract Pre-synthesized morphologically tailored size and shape selective silver nanoparticles (AgNPs) decorated on bismuth molybdate support (AgNPs/α–Bi2Mo3O12) using simple wet impregnation method was employed. The prepared AgNPs/α-Bi2Mo3O12 nanocatalysts were tested in the selective partial oxidation of propylene to acrolein reaction. The introduction of well-defined size and shape of AgNPs on α–Bi2Mo3O12 is greatly promoted the strong metal support interactions (SMSI), creation of oxygen vacancies (Ov) and high propylene adsorption binding energy (calculated by DFT). The strong metal support interactions between Ag and α-Bi2Mo3O12 is clearly elucidated by the high quality HRTEM and STEM–HAADF microscopic images. In addition, surface atomic molar ratio measured by XPS analysis determined the key redox properties of AgNPs/α–Bi2Mo3O12 system and their influence on the overall catalytic efficiency in the oxidation of propylene via reduction of Mo6+ to Mo5+ initiated at low temperatures in Ag/α–Bi2Mo3O12 system. The Mo reduction is further confirmed by the activated oxygen removal from the MoO42– moieties after Ag incorporation on α–Bi2Mo3O12. Thus, confirmed the oxidation reaction pathway follows a Mars–van–Krevelen process. Further, DFT calculations supported the propylene adsorption is more favorable over Ag/α–Bi2Mo3O12 than bare α–Bi2Mo3O12 support. The propylene oxidation performance over Ag/α–Bi2Mo3O12 system was 5.5 times higher than bare α–Bi2Mo3O12 support, probably due to an enabled strong metal support interaction and increased oxygen vacancies.Abstract Pre-synthesized morphologically tailored size and shape selective silver nanoparticles (AgNPs) decorated on bismuth molybdate support (AgNPs/α–Bi2Mo3O12) using simple wet impregnation method was employed. The prepared AgNPs/α-Bi2Mo3O12 nanocatalysts were tested in the selective partial oxidation of propylene to acrolein reaction. The introduction of well-defined size and shape of AgNPs on α–Bi2Mo3O12 is greatly promoted the strong metal support interactions (SMSI), creation of oxygen vacancies (Ov) and high propylene adsorption binding energy (calculated by DFT). The strong metal support interactions between Ag and α-Bi2Mo3O12 is clearly elucidated by the high quality HRTEM and STEM–HAADF microscopic images. In addition, surface atomic molar ratio measured by XPS analysis determined the key redox properties of AgNPs/α–Bi2Mo3O12 system and their influence on the overall catalytic efficiency in the oxidation of propylene via reduction of Mo6+ to Mo5+ initiated at low temperatures in Ag/α–Bi2Mo3O12 system. The Mo reduction is further confirmed by the activated oxygen removal from the MoO42– moieties after Ag incorporation on α–Bi2Mo3O12. Thus, confirmed the oxidation reaction pathway follows a Mars–van–Krevelen process. Further, DFT calculations supported the propylene adsorption is more favorable over Ag/α–Bi2Mo3O12 than bare α–Bi2Mo3O12 support. The propylene oxidation performance over Ag/α–Bi2Mo3O12 system was 5.5 times higher than bare α–Bi2Mo3O12 support, probably due to an enabled strong metal support interaction and increased oxygen vacancies