Green Oxidation Of Tetradecane Catalyzed By The Noble-Metal Ru-substituted Polyoxometalates

N-alkanes have higher content in the oil and coal, but have less directly use value. In the process of conversion of alkane, in order to increase the additional value, lower the cost and reduce environmental pollution considering the relatively inert C-H bond and hard self-oxidation of alkane, green catalytic oxidation of tetradecane should receive considerable attention from the perspective of the megatrends of establishing green chemical processes. However, many methods are developed to strengthen the activity of C-H bond in the N-alkanes and have certain defects in that they usually need sacrificial oxidants, additives, solvents, or drastic conditions(high temperature and high pressure). It is relatively easier to achieve the oxidation of tetradecane by using hydrogen peroxide, alkyl peroxide, or iodosobenzene in comparison with oxygen and air, meanwhile, additional additives and the appropriate solvent had a certain influence on the activity of the catalysts which can catalyze and oxidize of tetradecan. However, we got a lot of targeted products as well as by-products and the toxic solids as well as waste liquids needed to be handled generated in the above processes, we have to face some inherent drawbacks such as low conversion rate, low efficiency, higher operating costs, and especially the increasingly stringent environmental problems. Therefore, it is an urgent problem to design and prepare new efficiently heterogeneous catalysts for the green catalytic oxidation of tetradecane.Ruthenium atom has the widest change of the oxidation state in the periodic table(from-2 to +8) owing to the 4d75s1 electronic structure, which make the ruthenium-containing compound own a unique redox property and excellent catalytic activity.Few reports currently reported the Ru-substituted polyoxometalates as oxidation catalysts, especially in the catalytic oxidation of tetradecane. Our group recently reported Ru-supported polyoxometalate [RuIV4(μ-O) 4(μ-OH) 2(H2O) 4(γ-SiW10O36) 2] 10-, which anchored on SBA-15 acting as catalyst for the green catalytic oxidation of tetradecane for the first time. In the absence of additives and solvents, the conversion rate of tetradecane in this process reached nearly 40% and we preliminarily realized the green catalytic oxidation of tetradecane. While, the development of the high efficient catalyst of green catalytic oxidation of tetradecane is still in a preliminary stage, it is worthy to further study this research for our chemical researchers.Based on the above ideas, we have commenced the following three parts in this paper:1. In the first part, we designed a novel Ru-containing polyoxometalate Na6(TMA) 2 [Te2W20O70(RuC6H6) 2] ? 25H2 O using the [RuC6H6Cl2]2 as the source of ruthenium, and then anchored on the functionalized mesoporous materials SBA-15 making a new type of heterogeneous catalyst and deeply explored its multi-phase green catalytic oxidation of tetradecane. The results showed that this solid catalyst represented the higher conversion rate(47.9%) for the oxidation of tetradecane under the optimal conditions.2. In the second part, we fabricated a Ru-containing Dawson-type polyoxometalate Cs3(NH4)[{Ru4O6(H2O)9}2Bi2W20O68(OH)2]?21H2O using the Ru(NH4)2Cl6 as the source of ruthenium,and then anchored on the functionalized mesoporous materials SBA-15 making a new type of heterogeneous catalyst and deeply explored its multi-phase green catalytic oxidation of tetradecane. The results showed that this solid catalyst represented the higher conversion rate(38.7%) for the oxidation of tetradecane under the optimal conditions.3. In the third part, we got a Ru-containing and Ni-containing sandwich-type polyoxometalate cluster(C2H8N)8 [(SiW11Ni(H2O)2O39)2Ru]?5H2O using the RuCl3 as the source of ruthenium, and then anchored on the functionalized mesoporous materials SBA-15 making a new type of heterogeneous catalyst and deeply explored its multi-phase green catalytic oxidation of tetradecane. The results showed that this solid catalyst represented the higher conversion rate(37.1%) for the oxidation of tetradecane under the optimal conditions.In summary, we designed and synthesized three kinds of polyoxometalate catalysts containing noble-metal ruthenium using different sources of ruthenium and explored its catalytic role in the green catalytic oxidation of tetradecane. We investigated the factors of reaction time, temperature, amount of catalyst, and the amount of catalyst loaded on the SBA-15 for the green catalytic oxidation of tetradecane and found the optimum catalytic conditions. Moreover, we also investigated the reuse of heterogeneous catalysts.