Polimer Uyarımlı Kolloid Agregasyonu Yöntemi ile Monodispers-Gözenekli Mikrokürelererin Sentezi ve Katalitik Uygulamaları
Özet
Carbon and nitrogen doped mesoporous, gravel-like TiO2 microparticles (m-CN/TiO2) were synthesized by the "polymer induced colloid aggregation" (PICA) method. These microparticles decorated with Pd nanoparticles were used as catalysts in Suzuki-Miyaura reaction conditions, and a yield close to 100% was obtained after 4 hours at 80oC. Then, m-CN/TiO2 microparticles were synthesized by PICA method and decorated with Ni-Pt nanoparticles (Ni-Pt/m-CN/TiO2) and used as photocatalyst in the dehydrogenation of hydrazine hydrate. Ni-Pt/m-CN/TiO2 microparticles, which is a heterogeneous catalyst with defective structure, high Ti(III) content (40.25%), high oxygen vacancy concentration (39.14%) and low band gap energy, Ti(III) content and oxygen vacancy concentration were significantly increased due to the defective, C, N rich structure of m-CN/TiO2 microparticles, since such an increase was not observed with a conventional TiO2 support material. The charge imbalance induced by Ti(III) species was found to promote the formation of oxygen vacancies on the surface of m-CN/TiO2 microparticles. The unique approach based on the deposition of Ni-Pt nanoparticles by PICA in the presence of C, N doped-mesoporous TiO2 based support via NaBH4 reduction allowed to obtain a heterogeneous catalyst with low band energy (1.7eV) for hydrogen production. Ni-Pt/m-CN/TiO2 microparticles were also tested as a photocatalyst for the photocatalytic dehydrogenation of hydrazine hydrate under visible light at 293 K. According to the reports for the photocatalytic dehydrogenation of hydrazine hydrate, the highest TOF was obtained as 530.1 h-1 at 100% H2 selectivity. This shows that m-CN/TiO2 microparticles synthesized by PICA method can be used as support material in both reaction types. Then, monodisperse-porous TiO2 and CeO2 microspheres were decorated with PdAu nanoparticles in bimetallic form (PdAu@TiO2 and PdAu@CeO2) by multi-step hydrolysis-condensation method and multi-step sol-gel molding method, respectively, and evaluated as photocatalysts for hydrogen production by visible and UV light-based formic acid dehydrogenation at room temperature for the first time. The highest TOF value in formic acid dehydrogenation under visible light was obtained with PdAu@TiO2 microspheres as 1391 h−1. This value is considerably higher than the similar catalysts used previously at room temperature. Due to the alloy formation resulting from the use of PdAu as bimetallic and visible light, 6.2 times higher hydrogen production rate was obtained with PdAu@TiO2 microspheres under visible light compared to monometallic Pd@TiO2 microspheres used in the dark. As a result, a new generation catalyst family with high yield and unique properties was synthesized for both green hydrogen production from different sources and Suzuki-Miyaura reaction.
