Preparation And Characterization Of New Nanostructured Catalysts For The Oxidative Dehydrogenation Of Propane To Propylene And Direct Synthesis Of Hydrogen Peroxide

The research drive to develop an oxidation dehydrogenation (ODH) process for propane comes from the facts that the chemical industry depends heavily on the propylene and other alkenes feedstock. The major source of propylene currently is steam cracking and FCC, the steam cracking maximizes ethylene yield and in the FCC plant propylene is produced as a by-product, so propylene production from these sources will barely match the consumption. Thermal dehydrogenation suffers from several drawbacks, such as thermodynamics limited, rapid coking and high reaction temperature, from the industrial standpoint. ODH can be a viable route for production alkenes as the presence of oxygen counteracts the thermodynamic limitation and prevent coking. While this has been recognized for a long time, an industrially applicable process has not been developed, because secondary oxidation of alkanes to carbon oxides is very significant on most materials. Thus the yield of alkenes remained under 30%, far from satisfactory for commercial application. So it is necessary to develop other new efficient catalysis materials for the ODH of propane. Recently considerable interest has been focused on the potential applications porous solid of ordered mesoporous silica with pore walls of uniform width in the range 1-5 nm and controlled uniform pore diameters in the range 2.5-25 nm as periodic hosts for the preparation of mesoporous catalysts with chemically functionalized surfaces have been widely investigated in the past decade. SBA-15 is a newly discovered mesoporous silica molecular sieve with larger pore diameters, tunable uniform hexagonal channels and thick framework walls, which improve its thermal stability, so it is a promising new type of porous support for fabrication the catalyst for ODH of propane.As an important chemical product, hydrogen peroxide was widely used in many fields, such as the bleaching of the pulp and paper, environmental protection, chemical and food industry for it is an environmentally friendly oxidant. With the increase of the demand, the production of hydrogen peroxide has become more and more important. Currently, the commercial production of H₂O₂ is mainly based on a multistep process involving cyclic hydrogenation and oxidation of an alkyl anthraquinone in a complex working solution. This high-energy consuming process often has disadvantages, such as the cost of the quinone solvent system and the elaborate treatments required to remove degradation products due to non-selective hydrogenation. Hence, it is highly attractive to develop more economical and "green" processes that can allow the direct synthesis of H₂O₂. Although notable recent progress in this area is the use of noble metal based catalysts to achieve efficient production of H₂O₂ from mixtures of H₂/O₂, the latter process in particular has attracted recent interest due to its high safety.1 Mesostructured Co-SBA-15 Catalysts for Oxidative dehydrogenation of propaneThe influence of cobalt loading (10-30 wt%), cobalt precursor on the physico-chemical and catalytic properties of mesoporous Co/SBA-15 catalysts for the light alkanes (propane and ethane) ODH reactions has been investigated. The combination of different techniques (LAXRD, WAXRD, Raman, TEM, and H₂-TPR) in the characterization of cobalt supported on mesoporous SBA-15 catalysts show that the disparity and the nature of the cobalt species depend strongly on the Co loading and cobalt precursor. Textural, TEM, and LAXRD results indicate that the ordered hexagonal mesoporous structure with large pore diameters of the support is retained upon the cobalt incorporation, and therefore high surface areas were obtained on the final catalysts. A maximum light alkenes (propylene and ethylene) yield was found for the sample with 20 wt% Co loading, though the activity test in the range of Co loading study. And with the similar cobalt loading (20wt%), the catalyst prepared from cobalt nitrate and citric acid has a better light alkenes formation rate than using other precursors. The high performance of the catalyst (prepared from cobalt nitrate and citric acid) in light alkanes (propane and ethane) oxidative dehydrogenation has been attributed to a better Co dispersion and a stronger cobalt-support interaction in final samples, as evidenced by TEM, XPS, and TPR.Cobalt catalysts impregnated on Zr and Ti-doped mesoporous SBA-15 silica were characterized and investigated in the oxidative dehydrogenation (ODH) of propane. Catalysts supported on pure siliceous SBA-15 and conventional amorphous silica were also examined. The best performance in propane ODH is achieved with the Co/Zr-SBA sample with 2wt% Zr. The enhanced catalytic performance of the Co/Zr-SBA catalysts has been attributed to the beneficial generation of highly dispersed Co²⁺-riched Co₃O₄ nanocrystallites in the zirconium-containing materials.2 ODH of propane over silica supported binary V-Mo-O catalystThe catalytic performance of vanadia dispersed on silica containing a nominal molybdena near-monolayer coverage in the oxidative dehydrogenation (ODH) of propane was investigated. The surface structure of the MO_x species (M = Mo, V) was probed with UV-laser Raman spectroscopy, while the acidity and reducibility of the materials were investigated by temperature programmed NH₃ desorption and H₂ reduction. The lattice oxygen content was test by propane pulse reaction. The great activity of vanadia dispersed on molybdena modified silica reflects the high activity of propane dehydrogenation rate. The high dispersion of V and Mo species, the interaction between the V, Mo species and the support, as well as the medium strong acidity of the catalysts all account for the high activity of this material.Vanadia catalysts supported on molybdena modified silica at theoretical monolayer coverage were tested in the oxidative dehydrogenation of propane. Characterization of the materials showed that MoO_x and VO_x surface species are essentially amorphous in nature and well dispersed on the support surface in isolated and polymeric moieties. V/Mo/Si catalysts were more active than V/Si or Mo/Si catalysts in the oxidative dehydrogenation of propane. There were no correlation between reducibility, determined by TPR, and activity was established, since all catalysts exhibited similar reduction behavior with T_max ranging between 470 and 510℃, but different activity. Comparing catalysts on propane pulse reaction, we could correlate the lattice oxygen species and the catalytic property, which suggests that the dispersion of vanadia on Mo modified silica near monolayer coverage could increase the catalyst activity for propane ODH reaction. The high activity can be ascribed to the formation of V-O-Mo bonds between the dispersed vanadia and the Mo modified layer. The results also reveal that the metal oxide can be well dispersed on modified neutral support material.3 Direct synthesis of hydrogen peroxide from H₂ and O₂ over nano-Pd/C catalyst The influence of support physico-chemical properties and reduce method on the catalytic properties of Pd/AC catalysts for the direct synthesis of hydrogen peroxide from H₂ and O₂ has been investigated. The catalytic reactions of hydrogen and oxygen molecules with active metal atoms of a catalyst for direct formation of hydrogen peroxide product and water has been presented. The combination of different techniques (XRD, SEM, TEM) in the characterization of active carbon support and the corresponding Pd/C catalysts show that the disparity and the nature of the surface characteristics of the carbon support play important roles in determining the final properties of the palladium loaded catalyst.Coupled with the theoretical analysis of Pd nanocrystals having different surface structures, it is further revealed that the crystal phase (110) having a linear alignment of metal atoms on the crystals is more effective for selective H₂O₂ formation from H₂ and O₂, which is suggested to be one of the most important parameter that must be considered in designing highly effective Pd catalyst for direct H₂O₂ synthesis.4 Direct production of hydrogen peroxide from CO, O₂, and H₂O over a novel alumina-supported Cu catalystCurrently, the commercial production of H₂O₂ is mainly based on a multistep process involving cyclic hydrogenation and oxidation of an alkyl anthraquinone in a complex working solution. This high-energy consuming process often has disadvantages, such as the cost of the quinone solvent system and the elaborate treatments required to remove degradation products due to non-selective hydrogenation. it is highly attractive to develop more economical and "green" processes that can allow the direct synthesis of H₂O₂ from H₂ and O₂ or from CO, O₂ and H₂O, in particular the later process has attracted recent interest due to its high safety.The influence of support, reduction method, active metal for the direct synthesis of hydrogen peroxide from CO, O₂ and H₂O has been investigated. A series of environmentally benign nanocrystalline Cu/Al₂O₃ catalysts for the direct formation of H₂O₂ from CO, H₂O and O₂ have been developed by a novel liquid-phase chemical reduction method and characterized by TEM, XRD, and N₂O titration. A maximum H₂O₂ formation rate of 0.236 mmol(g-cat.)^-1h^-1 was achieved over the catalyst with average Cu particle size of ca. 15 nm, suggesting the presence of a significant size effect for the performance of the Cu/Al₂O₃ catalysts.