Natural clay nanotube-metal based core/shell catalysts for hydroprocesses: structural design, synthesis, applications.

A self-assembly of clay nanotubes in functional arrays for the production of organized organic/inorganic heterostructures is described. These 50-nm-diameter natural alumosilicate nanotubes are biocompatible. Halloysite allows for 10–20 wt % chemical/drug loading into the inner lumen, and it gives an extended release for days and months (anticorrosion, self-healing, flame-retardant, antifouling, and antibacterial composites). The structured surfaces of the oriented nanotube micropatterns enhance interactions with biological cells, improving their capture and inducing differentiation in stem cells. An encapsulation of the cells with halloysite enables control of their growth and proliferation. This approach was also developed for spill petroleum bioremediation as a synergistic process with Pickering oil emulsification. We produced 2–5-nm-diameter particles (Au, Ag, Pt, Co, Ru, Cu–Ni, Fe3O4, ZrO2, and CdS) selectively inside or outside the aluminosilicate clay nanotubes. The catalytic hydrogenation of benzene and phenol, hydrogen production, impacts of the metal core–shell architecture, the metal particle size, and the seeding density were optimized for high-efficiency processes, exceeding the competitive industrial formulations. These core–shell mesocatalysts are based on a safe and cheap natural clay nanomaterial and may be scaled up for industrial applications.

Self-assembly of ordered silica arrays on clay nanotubes resulted in mesoporous MCM-41 type materials with enhanced catalytic properties.

Mesoporous silicas of MCM-41 type modified by transition metal oxides, such as molybdenum, vanadium, and tungsten, were synthesized. These materials were characterized by low-temperature nitrogen adsorption/desorption, Fourier transform infrared spectroscopy, X-ray spectral fluorescence analysis, and transmission electron microscopy techniques and applied for the removal of sulfur compounds in model and real fuels by oxidative desulfurization. The catalysts obtained were tested under optimal conditions. Dibenzothiophene was removed completely, and sulfur removal in gasoline and diesel fractions could reach 91 and 63%, respectively. These catalysts retain their activity in gasoline fraction desulfurization for 5 cycles.