The light olefins, important raw materials in the petrochemical industry, were produced from the steam or catalytic naphtha cracking and dehydrogenation process. Those processes were not sufficient to meet the demand for olefins due to the various restrictions such as endothermic reaction, deactivation by coke formation, and high energy consumption. The demand for light olefins including ethylene, propylene, butenes, and butadiene (BD) was increased gradually and thus need new processes for producing light olefins efficiently. The oxidative dehydrogenation (ODH) process could be an alternative way to produce butenes or BD from n-butane or n-butenes.
In this study the ODH of 1-butene over the bismuth-molybdate based multicomponent oxide catalysts had been carried out to produce BD in the fixed-bed reactor at ambient pressure. Various catalysts and operating conditions had them tested to optimize the catalytic activity in the ODH of 1-butene. When the molar ratio of Bi/Mo was 1 (? phase, Bi2Mo2O9), it was shown the best catalytic activity in the ODH reaction. Thus, the molar ratio of Bi/Mo = 1 fixed and investigated the effects of various parameters.
BiFexMo oxide catalysts were prepared by co-precipitation and their activities towards promoting the ODH of 1-butene were tested. The catalytic activity in the ODH reaction was dependent on their catalyst composition. The peak area of temperature programmed reduction of 1-butene (1-C4H8-TPD) and successive oxidation (TPRO) was dependent on Fe contents in BiFexMo oxide and was maximized at x = 0.65, which therefore showed the greatest oxygen mobility. The oxygen mobility were likely correlated with butene conversion and BD selectivity, which reached 69% and 91%, respectively, after reaction for 14 h over the BiFe0.65Mo oxide catalyst.
It was known that the phosphorous played a role of improving of the catalyst''s stability. A series of BiFe0.65MoPx oxide catalysts with varying phosphorous contents were prepared and ODH of 1-butene was carried out. Among the catalysts studied, BiFe0.65MoP0.1 oxide catalyst showed the highest conversion and selectivity to BD. The higher catalytic activity originated likely from acidity of BiFe0.65MoP0.1 oxide catalyst and its acidity was higher than that of phosphorous free oxide catalyst and further contained other oxide catalysts. Also, the higher catalytic activity was related with the amount of weakly bounded intermediate and the desorbing temperature of strongly bounded intermediates. BiFe0.65MoP0.1 oxide catalyst was stable and no significant deactivation for 100 h ODH reaction was shown. The catalytic activity of the catalysts in the ODH reaction was dependent on the pH value employed during catalyst preparation. The BiFe0.65MoP0.1 oxide catalysts were prepared and investigated the effect of pH on the catalytic activity of the catalysts. It was found that the catalytic performance of the catalysts depends on the pH of metal solution and the catalyst prepared at pH 5 exhibits the best catalytic activity. TPRO measurements showed that the catalytic performance was related to the oxygen mobility of the catalyst. The TPRO peak temperature showed the lowest value on BiFe0.65MoP0.1 oxide catalyst prepared at pH 5, and was shifted to higher temperature with increasing pH value employed. The influences of phosphorous precursors on the catalytic activity of the BiFe0.65MoP0.1 oxide catalysts in the ODH of 1-butene were studied. The catalytic activity depended on the nature of phosphorous precursors. The BiFe0.65MoP0.1 prepared from a phosphoric acid precursor was showed the best catalytic activity. Based on the results of TPRO experiments, the catalytic activity was proposed to be associated with the ability for re-oxidation of the catalysts.
The influence of the catalyst composition of the BiVxMo1-x oxide catalysts for ODH of 1-butene had been studied. It was found that the catalyst composition has a strong influence on its activity. The conversion of 1-butenes over BiVxMo1-x oxide catalysts showed volcano-shaped curves with respect to the vanadium content. Among the catalyst studied, the BiV0.6Mo0.4 oxide catalyst showed the highest catalytic activity. The catalytic activity of the catalysts was elucidated by TPRO and 1-C4H8-TPD experiments. It was revealed that the catalytic activity of the BiVxMo1-x oxide catalysts was attributed to the oxygen mobility, the quantity of lattice or surface oxygen, and the degree of easy desorption of BD. In addition, the BiV0.6Mo0.4 oxide catalyst was stable and no deactivation during the 90 h ODH reaction was shown.
BiFe0.65NixMo oxide catalysts were prepared and applied for the ODH of 1-butene. TPRO measurements revealed that the catalytic activity was closely related to the oxygen mobility. The yield in BD increased with decreasing the oxygen mobility of the catalysts. A small amount of nickel content improved the catalytic activity; however, a higher amount of nickel content led to a decrease in the catalytic activity and in the combustion reaction to CO2. BiFe0.65Ni0.05Mo oxide catalyst showed the highest conversion and BD yield due to the high oxygen mobility. The BiFe0.65Ni0.05Mo oxide catalyst was very stable and no deactivation during the 100 h reaction was shown.
BiFe0.65Me0.05Mo oxide catalysts promoted with different metals (Me = Ni, Co, Zn, Mn, and Cu) were prepared employing the co-precipitation method. The effects of the metal addition on their catalytic activity for the ODH of 1-butene had been investigated. It had been found that the catalytic activity of BiFe0.65Me0.05Mo oxide catalysts depends on the nature of the metals employed, varying in the order of Ni > Co > Zn > Mn > Cu, with the Ni-promoted catalyst having the best catalytic activity, for the given reaction conditions. TPRO measurements revealed that the catalytic activity of the BiFe0.65Me0.05Mo oxide catalysts was well correlated with the oxygen mobility of the catalysts. The CO2 selectivity of the catalysts was related to their combustion sites depends on the nature of metals.