The development of robust synthetic routes to stable covalent organic frameworks (COFs) is important to broaden the range of applications for these materials. We report here a simple and efficient three-component assembly reaction between readily available aldehydes, amines, and elemental sulfur via a C–H functionalization and oxidative annulation under transition-metal-free conditions. Five thiazole-linked COFs (TZ-COFs) were synthesized using this method. These materials showed high levels of crystallinity, high specific surface areas, and excellent physicochemical stability. The photocatalytic applications of TZ-COFs were investigated, and TZ-COF-4 gave high sacrificial hydrogen evolution rates from water (up to 4296 μmol h–1 g–1 under visible light irradiation) coupled with high stability and recyclability, with sustained hydrogen evolution for 50 h.

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Abstract:The alkylation of benzene by propane to yield isopropylbenzene (iPrPh) was studied using bifunctional Pd-acid catalysts, such as Pd-heteropoly acid and Pd-zeolite, in a fixed bed reactor at 300 • C and 1 bar pressure. Keggin-type tungstosilicic acid H 4 SiW 12 O 40 (HSiW) and zeolite HZSM-5 were used as the acid components in these catalysts. The reaction occurred most efficiently over 2%Pd/25%HSiW/SiO 2 , giving iPrPh with up to 88% selectivity. The Pd-HSiW catalyst was more selective than the Pd-HZSM-5; the latter gave only 11-18% iPrPh selectivity. The reaction proceeded via a bifunctional mechanism including the dehydrogenation of propane to form propene on Pd sites, followed by the alkylation of benzene with the propene on acid sites. The effect of Pd loading in Pd-HSiW and Pd-HZSM-5 catalysts indicated that the first step reached quasi-equilibrium at 1.5-2% Pd loading and the second step became rate limiting. The addition of gold to Pd-HSiW enhanced the activity of this catalyst, although the Au-HSiW without Pd was inert.

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