Selective gas conversion of isopropyl alcohol over silver nanoparticles (Ag-NPs) supported on new mesoporous silica precipitated from natural resources
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A series of silver nanoparticles (Ag-NPs) loaded onto new mesoporous silica (MS), produced from natural cheap pumice was prepared via wet impregnation and characterized by means of several analytical techniques. Catalysts Ag–x/MS with x = 3, 10 and 20 wt% have been investigated in the gas conversion of isopropyl alcohol (IPA) under N2 and air atmospheres and exhibit a particular catalytic behavior different from conventional crystalline and supported silver-based catalysts. In N2 atmosphere, Ag–x/MS catalysts provide propene by dehydration process with selectivity greater than 95% whereas under the air atmosphere at low temperature (≤ 423 K), the reaction only produces acetone by oxidative dehydrogenation. This bifunctionality was due to special textural properties of MS support, characterized by high specific surface area (423 m2 g−1) and Bronsted acidic sites which are formed by bridged siloxanes (≡Si–O–Si≡) and silanols groups (≡Si–OH) leading to the formation of propene and on the other hand, to the high dispersion and redox properties of Ag-NPs under air atmosphere giving rise to “Ag-Ox” species which are selectively active for acetone production. The selective oxidative dehydrogenation toward acetone was confirmed by the non-detection of total oxidation products (CO/CO2) suggesting that the MS support preserves Ag-NPs against agglomeration and the redox properties of surface active “Ag-Ox” during the long-time service. The exceptional surface characteristics of MS produced from pumice and its promoting effect in the dispersion of active metal elements in the conversion of IPA exceeds broadly those obtained on various silica supports reported in the literature.
KeywordsSilver nanoparticles Isopropyl alcohol conversion Silver-loaded mesoporous silica Dehydration Oxidative dehydrogenation
This research was supported financially by the University of Mohammed V, Morocco under the Project No. SCH 04/09, and by the Hassan II Academy of Science and Technology, Morocco. The authors thank Pr. M. KACIMI for his assistance and contribution to catalytic tests.
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