Nowadays, most of the researches are focused on metal nanoparticles. They have unique properties on magnetic, electronic, optical and chemical behavior compared to bulk materials, because of their large surface area to volume ratio. To solve these problems it would be better to immobilize them on suitable support materials and use them as heterogeneous catalysts. Therefore, most of current researches are focused on modification of different supports for immobilization of metal nanoparticles. However, inorganic solids such as silica, carbon, clay, zeolites and mixed oxides are widely used to carry metal nanoparticles. Liquid-phase oxidation of methyl aromatic hydrocarbons is of great scientific, technological, and commercial importance. One of the most successful commercial applications is the production of terephthalic acid (TA) by liquid-phase oxidation of p-xylene (PX) with air over a Co-Mn-Br catalyst system in acetic acid (HOAc) at 150-210 °C. As practiced, this reaction is known as the MC (Mid-Century) process. For the last several years, the kinetics of the reaction network and the process engineering aspects of the MC process of PX oxidation have been investigated in details. The free-radical chain mechanism, as a general framework within which the kinetics features of hydrocarbon oxidation in liquid phase are interpreted, is now generally accepted. The efficacy of the Co-Mn-Br catalyst system is due to the synergistic effect of the coupled catalytic cycles of cobalt, manganese, and bromide. In this work, synthesis and characterization of a new bentonite supported catalyst is reported. In this regard, Na-bentonite was modified in two steps. At the first step, the Na-bentonite was modified with cetylpyridinium bromide (CPB) as a monolayer and then this monolayer bentonite treated with the second generation of an amidoamine cascade, named 3, 3'-(dodecylazanediyl) bis(N-(2-(2,3,3'-(dodecylazanediyl)bis(N-(2-(2-aminoethyl(2-hydroxy benzenimine))ethyl)propanamide) (DAEP) for preparation of a modified bilayer bentonite (Ben-DAEP-modified). The new host–guest catalyst was prepared by immobilization of Co 2+ , Mn 2+ or Co 2+ /Mn 2+ on the Ben-DAEP-modified. The solid catalysts characterized by FT-IR, SEM, BET, XRD, XRF, TEM and CHN. Reaction conditions are optimized for oxidation by varying temperature, pressure, amount of catalyst, time and relation between catalyst and oxidant. This is the first report on performing this reaction with nanocatalysts. The reaction did not proceed in the absence of the catalyst. The optimum conditions for this reaction are: 0.15g catalyst which is contains Co/Mn = 10/1, 3% w Br - as promoter, 190 o C, 17 atm, and 3h. Overall conversion is 100% and the selectivity for terephthalic acid is more than 97%. These results have shown that this research is a successful attempt for oxidation of p -Xylene.
