1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 z Catalysis Phenyltetrazole as a New Ligand for Immobilization of Palladium Nanoparticles on SBA-15: A New Robust Catalyst with High Loading of Pd for Rapid Oxidation and Reduction Firouz M. Moghaddam,* Vahid Saberi, and Pedram Kalvani [a] In this work, a new catalyst based on palladium nanoparticle supported SBA-15 has been introduced. The designed catalyst was characterized by Scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FT-IR), Brunauer–Emmett–Teller (BET) surface area analysis, thermo gravimetric analysis (TGA), Energy-dispersive X-ray spectroscopy (EDS) and atomic absorp- tion spectroscopy (AAS) analyses. For the first time, phenyl- tetrazole has been used as a ligand to the functionalization of SBA-15 to design robust heterogeneous catalyst with high- loading metal for reduction and oxidation in short time using a low amount of the catalyst. Introduction In recent years, trends and demands toward sustainable chemistry and environmentally benign processes led to design heterogeneous catalyst system that exhibit in high activity and selectivity with long-term stability and reusability. [1–4] In many cases, stable supporting ligands, complexes and other catalytic species onto nanostructured material for the design robust heterogeneous catalyst with higher efficiency has been designed. [5–7] Among nanostructured materials, silica mesopo- rous materials for their surface area, higher stability and easily synthesized are most popular for above purpose. SBA-15 as mesoporous silica with 2D channels and higher stability in comparison to other types mesoporous silica such as MCM is an excellent choice for catalytic cases and can be easily functionalized with ligand due to having hydroxyl groups on its surfaces. [8–10] Supporting a ligand to a heterogeneous surface for immobilization of transition metals such as palladium and copper is a well-known method for designing efficient catalyst. The ligands used for this surface must be stable to high- temperature, air, moisture and aqueous solution. [11–14] Tetrazoles can be prepared through a cyclization process. These simple 4 nitrogen-containing heterocycles may act as polydentate ligands for immobilization of transition metal, because of their aromaticity, excellent coordination capability and the possibility of offering new functionalized materials. [15–19] Recently, there have been several reports on immobilization of Palladium nanoparticles on heterogeneous support applied in organic transformations. Pd Nanoparticles Immobilized on Supported Magnetic GO@PAMPS for Suzuki–Miyaura Coupling Reaction, [20] cellulose sponge for cross-coupling, [21] magnetic carbon dots@Fe 3 O 4 nanocubes for hydrogen generation, [22] nanoceria for dehydrogenation of formic acid, [23] core-shell nanogels for Mizoroki-Heck Reaction, [24] Magnetic nanocomposite for Suzuki reaction, [25] Fe3O4@g-AlOOH nanocomposite for reduction, [26] nitrogen-doped carbon microtubes for Suzuki reaction, [27] mesoporous silica-based nanotubes for oxidation [28] and meso- porous carbon nitride for oxidation [29] was reported. In 2006 Karimi and coworkers reported palladium nanoparticle immobi- lized on SBA-15 for oxidation of alcohols. [30] Recently several reports about Palladium immobilized on silica as heteroge- neous catalyst has been published. [31] Inspired by above fact, in this work we used tetrazoles as an efficient ligand onto SBA-15 for immobilization of palladium nanoparticle to generate a Pd@SBA-15/TET catalyst which was fully characterized. The catalytic activity of Pd@SBA-15/TET was subsequently inves- tigated in the oxidation and reduction reactions. The proposed ligand system featured a high stability, air and moisture insensitiveness being also simple in terms of preparation. Because the majority of the nanoparticles are usually formed inside the channels of ordered porous materials, the support prevents agglomeration. One of the most important advan- tages of our catalyst is high-loading of palladium on a catalyst that causes the short time of reaction and reduces the amount of catalyst and reductant for reaction. Results and Discussion Synthesis and characterization of catalyst The general route for the preparation of the catalyst is demonstrated in Scheme 1. SBA-15 initially prepared from hydrolysis and condensation of tetraethyl orthosilicate (TEOS) as silica source under an acidic condition in the presence of [a] Prof. F.M. Moghaddam, V. Saberi, P. Kalvani Laboratory of Organic Synthesis and Natural Products Department of Chemistry Sharif University of Technology Azadi Street, PO Box 111559516, Tehran, Iran E-mail: matloubi@sharif.edu Supporting information for this article is available on the WWW under https://doi.org/10.1002/slct.201800453 Full Papers DOI: 10.1002/slct.201800453 6779 ChemistrySelect 2018, 3, 6779 – 6785  2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim