Anthony Morena

Hollow silica nanospheres (NSs) are emerging as versatile supports for heterogeneous catalysis due to their high specific surface area and accessible internal cavities via the mesoporous shell. In this work, NS synthesis was optimized and group 13 metal cations (Al3+, Ga3+, In3+) were incorporated into the silica structure to tailor Lewis and Brønsted acidity. The influence of loading was investigated, selecting Al3+ as the target metal cation. Imidazolium functionalization yielded bifunctional catalysts. Materials were characterized by Transmission Electron Microscopy (TEM), Nitrogen Physisorption, Thermogravimetric Analysis (TGA), Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES), and Elemental Analysis (EA). Solid-state NMR spectroscopy was performed on 27Al, 71Ga, 13C, and 29Si nuclei, while the chemical environment of indium was investigated using X-ray Photoelectron Spectroscopy (XPS). 31P ssNMR with trimethylphosphine (TMP) as a probe molecule, and NH3-TPD analyses were performed to evaluate the acidity. All bifunctional solids were highly active catalysts for converting CO2 into cyclic carbonates via epoxide cycloaddition. The indium-doped bifunctional solid was the most efficient, showing stability and recyclability. Activity correlated with acid site nature and strength, offering insights into key design principles. The material remained active under different conditions and with different epoxides, showing competitive activity versus catalysts reported in the literature.

Carbon nanotubes have been covalently functionalized with catechol moieties through the formation of the corresponding aryl radicals obtained by reacting 4‐aminocatechol with isoamyl nitrite. The functionalized multiwalled carbon nanotubes have been in turn used to immobilize Pd(II) ions on its surface forming catechol‐Pd complexes, which were reduced to Pd nanoparticles (NPs). The so‐obtained hybrid material has been characterized by means of thermogravimetric analysis coupled with differential scanning calorimetry (TGA‐DSC), X‐ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). This latter technique allowed to estimate the nanoparticle size (5.7±2.8 nm) whereas a palladium loading of 20.3 wt % has been found by inductively coupled plasma optical emission spectroscopy (ICP‐OES). The carbon nanotube‐catechol‐Pd hybrid was used as catalyst in two C−C coupling reactions, namely Suzuki and Heck reactions, resulting recyclable for at least 9 times in the latter process. During the reuse Pd nanoparticles increase their dimension to 19.3±11.7 nm.

Three different carbon nanoforms (CNFs), single-walled and multi-walled carbon nanotubes (SWCNTs, MWCNTs) and carbon nanohorns (CNHs), have been used as supports for the direct polymerization of variable amounts of a bis-vinylimidazolium salt. Transmission electron microscopy confirmed that all CNFs act as templates on the growth of the polymeric network, which perfectly covers the nanocarbons forming a cylindrical (SWCNTs, MWCNTs) or spherical (CNHs) coating. The stability of these hybrid materials was investigated in the conversion of CO₂ into cyclic carbonate under high temperature and CO₂ pressure. Compared with the homopolymerized monomer, nanotube-based materials display an improved catalytic activity. Beside the low catalytic loading (0.05–0.09 mol%) and the absence of Lewis acid co-catalysts, all the materials showed high TON values (up to 1154 for epichlorohydrin with SW-1:2). Interestingly, despite the loss of part of the polymeric coating for crumbling or peeling, the activity increases upon recycling of the materials, and this behaviour was ascribed to their change in morphology, which led to materials with higher surface areas and with more accessible catalytic sites. Transmission electron microscopy analysis, along with different experiments, have been carried out in order to elucidate these findings.