Catalytic Dehydrogenation Of Isobutane Research Articles

Catalytic dehydrogenation of isobutane over supported MoOx/K-Al2O3

Potassium-promoted, alumina-supported molybdenum oxide is investigated for non-oxidative isobutane dehydrogenation, with an emphasis on sub-monolayer coverages. After pre-reduction in H2, initial isobutene turnover frequencies are largely independent of Mo loading, but deactivation rate constants increase by >100-fold as loadings increase to monolayer, leading to a >13-fold difference in reaction rates at extended time on stream. Mo oxidation state by in situ X-ray absorption spectroscopy is stable with time on stream, arguing against continued catalyst restructuring as the origin of deactivation. Across the set of loadings, isobutane dehydrogenation and coke formation are correlated with partially reduced Mo4+ and deeply reduced Moδ+ sites, respectively. Given the stable dehydrogenation activity of low-loaded Mo, in contrast to the rapid deactivation of high-loaded Mo, sub-monolayer metal oxides may warrant further investigation as light alkane dehydrogenation even when their bulk counterparts may not.

Zeolite membrane reactor for high-temperature isobutane dehydrogenation reaction: Experimental and modeling studies

Isobutylene has been produced by packed bed reactors (PBRs), but there is thermodynamic limitations and a critical need for efficient isobutylene production. Catalytic dehydrogenation of isobutane using a membrane reactor is a feasible solution because it helps in overcoming thermodynamic limitations as well as separates isobutylene by allowing H2 to selectively permeate through the membrane. In this study, isobutane dehydrogenation (IBDH) in a packed-bed membrane reactors (PBMRs) in combination with a Pt/Al2O3 catalyst was investigated. MFI zeolite membranes were found to have good H2/i-C4H10 selectivity which enhanced isobutane conversion at high operation temperature. The effect of the PBMR operating conditions such as weight hourly space velocity (0.8-2.7 h−1), temperature (500–650 °C), and sweep gas flow rate (0-40 cm3/min) on isobutane conversion, isobutylene selectivity and isobutylene yield was studied. The highest isobutane conversion, isobutylene selectivity and isobutylene yield was 27%, 97% and 26%, respectively, from experiments. We developed a 1D plug flow reactor model for the IBDH system and isobutane conversion was evaluated at a wider range of operating conditions. Isobutane conversion of >90% was from calculation obtained at practically meaningful operating conditions.

The catalytic dehydrogenation of isobutane and the stability enhancement over Fe incorporated SBA-15

Fe-incorporated SBA-15 catalysts were prepared via hydrothermal method using urea as self-regulator for pH. The obtained catalysts expressed highly ordered mesoporous structures proved by N2 adsorption-desorption, XRD and TEM characterization, also were tested for their activity in dehydrogenation of isobutane. Moderately and strongly acidic sites as well as Fe3+ species were identified as active sites. The ordered mesoporous iron-silica catalyst displayed better catalytic stability as compared with amorphous iron-silica catalyst, which was ascribed to the confinement effect of ordered meso-structure. Moreover, framework iron improved the interaction of iron with the support and increased more weakly acidic sites, which were favorable to restrain the coke formation. The coke was a major cause for catalytic deactivation.

Catalytic dehydrogenation of isobutane over a Ga2O3/ZnO interface: reaction routes and mechanism

In this work, physical mixtures of ZnO and Ga2O3, even with a small amount of Ga2O3, were found to exhibit greatly enhanced catalytic performance for isobutane dehydrogenation compared to their individual components, namely solely ZnO or Ga2O3.

Relationship between Cr-Al Interaction and the Performance of Cr-Al<sub>2</sub>O<sub>3 </sub>Catalysts for Isobutane Dehydrogenation

A series of catalysts were prepared using the kneading molding method and the impregnation method as well as the dry mix method by using different raw materials. By using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and temperature-programmed reduction (TPR) techniques, we studied the relationship between the catalyst performance and the Cr-Al interaction in the catalytic dehydrogenation of isobutane. The results demonstrated that the Cr-Al interaction in the catalyst had a direct influence on the catalytic activity and the selectivity of isobutene. The catalysts prepared using the kneading molding method had higher catalytic activity and isobutene selectivity than those prepared using the dry mix method. By comparison, XRD, XPS, and TPR results showed that the greater the Cr-Al interaction in the catalyst was, the higher the catalytic activity was. Here, we propose a mechanism of isobutane dehydrogenation.

Catalytic dehydrogenation of isobutane over Co-based catalysts

In this work, to optimize the catalytic performance of Co-based catalysts for isobutane dehydrogenation, the effects of support, calcination temperature and some promoters were investigated systematically. Results of activity tests and catalyst characterization jointly indicated that both the support and calcination temperature influenced Co dispersion, catalyst acid properties and the interaction between support and Co species significantly. Consequently, the adsorption–desorption behaviors for isobutane and isobutene as well as the dehydrogenation performance were further affected. Sulfided Co/SiO2, with no acidity, exhibited the best performance. Although high calcination temperature was beneficial for achieving a high selectivity to isobutene over Al2O3 and MgAl2O4 supported Co-based catalysts, the inevitable formation of Co2SiO4 over Co/SiO2 at high temperature led to reduced active sites and dehydrogenation activity. In addition, by comparing the different effects of the separate introduction of S, Sn, Cu and Cl, it was concluded that an efficient promoter should present the following characteristics: inhibition of the formation of metal ensembles, and strong binding affinity to two hydrogen atoms of one additive atom.

Catalytic dehydrogenation of isobutane in the presence of hydrogen over Cs-modified Ni 2 P supported on active carbon

• Ni 2 P catalyst is tested in dehydrogenation of isobutane for the first time. • The effects of Cs promoter on catalytic performance of Ni2P/AC were investigated. • Cs-Ni2P/AC exhibits high activity and selectivity for isobutane dehydrogenation. In this article, an environmentally friendly non-noble-metal class of Cs-Ni 2 P/active carbon (AC) catalyst was prepared and demonstrated to exhibit enhanced catalytic performance in isobutane dehydrogenation. The results of activity tests reveal that Ni/AC catalyst was highly active for isobutane cracking, which led to the formation of abundant methane and coke. After the introduction of phosphorus through impregnation with ammonium di-hydrogen phosphate and H 2 -temperature programmed reduction, undesired cracking reactions were effectively inhibited, and the selectivity to isobutene and stability of catalyst increased remarkably. The characterization results indicate that, after the addition of phosphorous, the improvement of dehydrogenation selectivity is ascribed to the partial positive charges carried on Ni surface in Ni 2 P particles, which decreases the strength of Ni C bond between Ni and carbonium-ion intermediates and the possibility of excessive dehydrogenation. In addition, Cs-modified Ni 2 P/AC catalysts display much higher catalytic performance as compared to Ni 2 P/AC catalyst. Cs-Ni 2 P-6.5 catalyst has the highest catalytic performance, and the selectivity to isobutene higher than 93% can be obtained even after 4 h reaction. The enhancement in catalytic performance of the Cs-modified catalysts is mainly attributed to the function of Cs to improve the dispersion of Ni 2 P particles, transfer electron from Cs to Ni, and decrease acid site number and strength.

Promoting mechanism of sulfur addition in catalytic dehydrogenation of isobutane over Mo/MgAl2O4 catalysts

Mo/MgAl2O4 catalysts with sulfur addition were verified to exhibit excellent performance in catalytic dehydrogenation of isobutane, which could yield up to 56.3wt% isobutene at 560°C. Catalyst characterization and activity test results jointly revealed that MoS2 formed during the induction period probably constituted the active phase for dehydrogenation. As to the formation of MoS2, treatment with appropriate reducing gases (e.g., CO) was required. However, in the atmosphere of H2, molybdate species were partially reduced to MoO2, which inhibited the formation of MoS2. Furthermore, Mo/MgAl2O4 catalysts sulfided by H2S/N2 exhibited a high initial activity, further confirming that MoS2 species were indispensable to dehydrogenation reaction. Stability evaluation of the Mo/MgAl2O4-S catalyst indicated that the catalytic activity decreased slightly within six reaction-regeneration cycles. The irreversible deactivation probably resulted from the obvious sulfur loss. Therefore, appropriate measures to replenish sulfur should be carried out in future commercial application.

Synergistic effect between Sn and K promoters on supported platinum catalyst for isobutane dehydrogenation

Catalytic dehydrogenation of isobutane has recently received considerable attention because of the increasing demand for isobutene. In this study, the synergistic effect between Sn and K on PtSnK/γ-Al 2O 3 catalysts has been investigated by changing the content of Sn. It was found that with the presence of potassium, suitable addition of Sn could not only increase the metal dispersion, but also reduce the catalyst acidity. In these cases, the synergistic effect could also strengthen the interactions between the metal and support, which resulted in an increase in both catalytic activity and stability. In our experiments, Pt-0.6SnK/A1 catalyst exhibited the lowest deactivation rate (12.4%) and showed a selectivity to isobutene higher than 94% at the isobutane conversion of about 45.3% after running the reaction for 6 h. However, with the excessive loading of Sn, surface property of active sites and the interactions between metal and support were changed. As a result, the initial optimal ratio between the metallic function and acid function would be destroyed, which was disadvantageous to the reaction.

Catalytic dehydrogenation of isobutane in the presence of carbon dioxide over nickel supported on active carbon

The dehydrogenation of isobutane to isobutene was carried out in the presence of carbon dioxide over the catalyst nickel supported on active carbon (AC). The state and property of nickel species (NiOx) in the catalyst are relevant to its calcination temperature, because NiO may be partially reduced to Ni by AC at high temperature. NiO and Ni species are different in the catalytic behaviors; Ni is only effective for direct dehydrogenation of isobutane, while NiO is also highly active for the coupled dehydrogenation with carbon dioxide. Carbon dioxide can significantly enhance the dehydrogenation of isobutane over NiO/AC through keeping NiO species, in situ eliminating hydrogen produced and suppressing coke formation.

Catalytic dehydrogenation of isobutane in the presence of carbon dioxide

The dehydrogenation of isobutane to isobutene in the presence and absence of carbon dioxide is discussed on the basis of catalytic studies. The V-Mg-O catalysts have been prepared using different preparation procedures. The structure and texture of the V-Mg-O catalysts were characterized by several techniques including X-ray diffraction (XRD), BET surface area measurements and infrared spectroscopy (IR). The results show that carbon dioxide enhances isobutane conversion in the reaction carried out over the V-Mg-O catalyst prepared by citrate method.

XPS and EXAFS study of supported PtSn catalysts obtained by surface organometallic chemistry on metals: Application to the isobutane dehydrogenation

In this work, well defined alumina and silica supported Pt and PtSn catalysts were prepared by surface organometallic reactions and were characterized by TEM, XPS and EXAFS. These catalysts were tested in the catalytic dehydrogenation of isobutane. XPS results show that tin is found under the form of Sn(0) and Sn(II,IV), being the percentage of Sn(0) lower for alumina supported than for silica supported catalysts. Tin modified platinum catalysts, always show a decrease of approximately 1 eV in the BE of Pt, what would be indicative of an electron charge transfer from tin to platinum. When the concentration of Sn(0) is high enough, in our case Sn(0)/Pt ∼ 0.3, EXAFS experiments demonstrated the existence of a PtSn alloy diluting metallic Pt atoms, for both PtSn/γ-Al 2O 3 and PtSn/SiO 2. This PtSn alloy seems to be not active in the dehydrogenation reaction; however, it is very important for selectivity and stability, inhibiting cracking and coke formation reactions. The ensemble of our catalytic, XPS and EXAFS results, show that bimetallic PtSn/γ-Al 2O 3 catalysts, prepared via SOMC/M techniques, can be submitted to several sequential reaction–regeneration cycles, recovering the same level of initial activity each time and that the nature of the catalytic surface remains practically without modifications.

Selective dehydrogenation of isobutane over supported Pt/Sn catalysts

Catalytic dehydrogenation of isobutane is important because of growing demand for isobutene as a precursor for the production of oxygenates required in reformulated gasoline. It was found that supporting tin and platinum in K-L-zeolite produces catalysts that exhibit high activity and selectivity for isobutane dehydrogenation. Furthermore, Pt/Sn/K-L-zeolite catalysts exhibit high resistance to deactivation at conditions conducive to high dehydrogenation conversions. Fundamental investigations of silica-supported Pt/Sn catalysts show that tin interacts with platinum to form Pt/Sn alloy particles, which reduces the size of surface Pt ensembles and inhibits the formation of highly dehydrogenated surface species required for the competing isomerization, hydrogenolysis, and coking reactions. Similarly, the addition of potassium to Pt/Sn/SiO 2 increases the selectivity for isobutane dehydrogenation by further reducing the size of surface Pt ensembles.

Computer-aided optimisation of catalytic dehydrogenation in packed-bed membrane reactor

Catalytic membrane reactors offer the opportunity to combine chemical reaction with the separation activity of the membrane in one unit operation. In order to determine suitable operating conditions, numerical simulations are performed and results obtained are compared to results from conventional reactor. The effects of the inner compartment radius and the reactor length are also investigated. The chemical reaction studied is the catalytic dehydrogenation of isobutane.

Production of isobutylene by catalytic dehydrogenation of isobutane

Several processes of paraffin dehydrogenation to olefins are reviewed. The NIIMSK process developed in the Soviet Union for dehydrogenation of isobutane in fixed and fluidized beds of catalyst is described. The technoeconomic indexes of the Soviet process are listed in comparison with advertising data on the Catofin process.

Aromatization of a C 4 alkane/alkene/hydrogen mixture obtained by catalytic dehydrogenation of isobutane

The aim was to establish whether there is competition between the dehydrogenation of an alkane to an alkene and its aromatization in the presence of hydrogen. The aromatization of the model compound isobutane was studied in two steps, firstly its catalytic dehydrogenation and secondly the direct thermal cracking of the dehydrogenation mixture at atmospheric pressure and at temperatures at which substantial aromatization of alkenes occurs. The role of hydrogen was studied by cracking mixtures of known composition. In all instances, the yields in aromatic hydrocarbons, although lower than expected, were higher than those obtained with the alkane. The inhibitory effect of hydrogen on aromatization was demonstrated.