Nickel Supported on Mesoporous Organosilica Nanoparticles Incorporating Pyridine-Based SNS Ligand as an Efficient Recoverable Catalyst for Chemical Fixation of CO2

In the light of metal-catalyzed CO2 cycloaddition to epoxides, the use of nickel catalysts with an excellent turnover number (TON) remained a challenge. In this study, we would like to report that mesoporous organosilica nanoparticle with pyridine-2,6-dicarboxylic thioester frameworks (SNS-MON) was found to be an excellent solid SNS-ligand for the preparation of new Ni catalyst (Ni@SNS-MON) for the mentioned CO2 conversion. The catalyst was first fully characterized by various techniques, for example, nitrogen adsorption-desorption analysis, transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), X-ray powder diffraction (PXRD) at a small angle, elemental analysis (CHNS), and inductively coupled plasma mass spectrometry (ICP-MS). After checking the various conditions, 0.1 mol % Ni@SNS-MON, 0.3 mol % TBAB as cocatalyst, and 10 bar CO2 at 100 degrees C were selected as the best reaction conditions for coupling of CO2 with styrene oxide with an excellent TON in terms of Ni centers. The catalyst could also selectively couple CO2 with various terminal epoxides within a short reaction time with excellent TON. To understand the accurate role of each component of the catalyst, the activity of Ni@NSN-MON was compared with some selected catalysts as well as a homogeneous analog of the Ni catalyst under identical reaction conditions. It is believed that the high activity and selectivity of Ni@SNS-MON can be related to the short channel of the catalyst, which accelerates mass transfer, and the strong binding of Ni centers to tridentate coordination of the SNS pincer ligand, which improves its Lewis acidic nature. The catalyst could be also recovered and reused for at least five reaction cycles without any decrease in its activity and selectivity.