Ultrafine Pt Nanoparticles on Defective Tungsten Oxide for Photocatalytic Ethylene Synthesis

The selective conversion of ethane (C2H6) to ethylene (C2H4) under mild conditions is highly wanted, yet very challenging. Herein, it is demonstrated that a Pt/WO3-x catalyst, constructed by supporting ultrafine Pt nanoparticles on the surface of oxygen-deficient tungsten oxide (WO3-x) nanoplates, is efficient and reusable for photocatalytic C2H6 dehydrogenation to produce C2H4 with high selectivity. Specifically, under pure light irradiation, the optimized Pt/WO3-x photocatalyst exhibits C2H4 and H2 yield rates of 291.8 and 373.4 µmol g-1 h-1, respectively, coupled with a small formation of CO (85.2 µmol g-1 h-1) and CH4 (19.0 µmol g-1 h-1), corresponding to a high C2H4 selectivity of 84.9%. Experimental and theoretical studies reveal that the vacancy-rich WO3-x catalyst enables broad optical harvesting to generate charge carriers by light for working the redox reactions. Meanwhile, the Pt cocatalyst reinforces adsorption of C2H6, desorption of key reaction species, and separation and migration of light-induced charges to promote the dehydrogenation reaction with high productivity and selectivity. In situ diffuse reflectance infrared Fourier transform spectroscopy and density functional theory calculation expose the key intermediates formed on the Pt/WO3-x catalyst during the reaction, which permits the construction of the possible C2H6 dehydrogenation mechanism.

Influence of the Au-Ti Active Site of the Titanosilicate MWW Zeolite on the Catalytic Activity of Ethane Dehydrogenation in the Presence of O2

The titanosilicate zeolite with a MWW topology structure was synthesized by the atom-planting method through the dehydrochlorination of the hydroxyl group in the deboronated ERB-1 zeolite (D-ERB-1) and TiCl₄, and Au was further loaded with the deposition precipitation method to apply for the ethane direct dehydrogenation (DH) and dehydrogenation of ethane in the presence of O₂ (O₂-DH). It was found that Au nanoparticles (NPs) below 5 nm exhibited good activity for ethane direct dehydrogenation and O₂-DH. The addition of titanium can not only anchor more Au but also make Au have a more dispersed homogeneous distribution. The ethane O₂-DH catalytic performances of Au-loaded Ti-incorporated D-ERB-1 (Ti-D-ERB-1) were compared to those of Au-loaded ZnO-D-ERB-1 and pure silicate D-ERB-1. The results confirm that ethane O₂-DH catalyzed by Au-Ti paired active sites is a tandem reaction of catalytic ethane DH and selective H₂ combustion (SHC) of generated H₂. According to the experimental results and calculated kinetic parameters, such as the activation energy of DH and SHC reaction heat of O₂-DH, SHC catalyzed by the Au/Ti-D-ERB-1 catalyst containing the Au-Ti active site can not only break the ethane dehydrogenation thermodynamic equilibrium limitation to improve the ethylene yield but also suppress the CO₂ and CO selectivity.

Development and Intensification of the Ethylene Process Utilizing a Catalytic Membrane Reactor

Ethylene is considered the most important petrochemical constituent in the world today. It is currently produced via the thermal cracking process, which is generally expensive. Ethane dehydrogenation (EDH) is endothermic, and the thermodynamic equilibrium limits its conversion. The present study explores the viability of using a catalytic membrane reactor (MR) for ethylene production from EDH. The removal of hydrogen from the reaction zone using a palladium-silver (Pd-Ag) membrane has led to a high shift in the equilibrium conversion. The effects of operating conditions and reactor configurations on the ethane conversion were investigated. The ultimate ethane conversion was 22.2% when using the MR at 660 K and 300 kPa. The ethane conversion in the shell-side of the reactor increased to ∼99% when benzene hydrogenation was added as an auxiliary reaction in the tube-side of the reactor. Two new processes for ethylene production were developed for an annual capacity of 100,000 metric tons. Cryogenic distillation was required to separate ethylene from ethane if there is no auxiliary reaction. On the other hand, the ethylene process with cyclohexane as a byproduct does not require a refrigeration cycle system, and its economic analysis shows a return on investment of 34.4%, indicating that the process is a promising technology.

Unravelling the redox mechanism and kinetics of a highly active and selective Ni-based material for the oxidative dehydrogenation of ethane

Bridging the gap between catalysis and reaction engineering during the kinetic analysis of the oxidative dehydrogenation of ethane over a highly active and selective Ni-based material.

C-H bond activation in light alkanes: a theoretical perspective

Alkanes are the major constituents of natural gas and crude oil, the feedstocks for the chemical industry. The efficient and selective activation of C-H bonds can convert abundant and low-cost hydrocarbon feedstocks into value-added products. Due to the increasing global demand for light alkenes and their corresponding polymers as well as synthesis gas and hydrogen production, C-H bond activation of light alkanes has attracted widespread attention. A theoretical understanding of C-H bond activation in light hydrocarbons via density functional theory (DFT) and microkinetic modeling provides a feasible approach to gain insight into the process and guidelines for designing more efficient catalysts to promote light alkane transformation. This review describes the recent progress in computational catalysis that has addressed the C-H bond activation of light alkanes. We start with direct and oxidative C-H bond activation of methane, with emphasis placed on kinetic and mechanistic insights obtained from DFT assisted microkinetic analysis into steam and dry reforming, and the partial oxidation dependence on metal/oxide surfaces and nanoparticle size. Direct and oxidative activation of the C-H bond of ethane and propane on various metal and oxide surfaces are subsequently reviewed, including the elucidation of active sites, intriguing mechanisms, microkinetic modeling, and electronic features of the ethane and propane conversion processes with a focus on suppressing the side reaction and coke formation. The main target of this review is to give fundamental insight into C-H bond activation of light alkanes, which can provide useful guidance for the optimization of catalysts in future research.

Insights into the electronic and redox behavior of surface-phosphated ceria catalysts in correlation with their propane oxydehydrogenation performance

In situ electrical conductivity measurements (ECMs) have been employed to gain insights into the redox and electronic behavior of ceria and surface-phosphated ceria catalysts with phosphorus contents lower than 2.2 at%. Temperature-programmed reduction under hydrogen (H2-TPR) was used to analyze the reducibility of the catalysts. Their propane oxydehydrogenation performance both in terms of activity and selectivity has been explained. It has been unambiguously shown that all the catalysts function via a heterogeneous redox mechanism involving only surface and subsurface lattice oxygen species whose availability and reactivity decrease with increasing phosphorus content with consequences on the catalytic performance.

Oxidative dehydrogenation of ethane: catalytic and mechanistic aspects and future trends

Ethane oxidative dehydrogenation (ODH) is an attractive, low energy, alternative route to reduce the carbon footprint for ethene production, however, the commercial implementation of ODH processes requires catalysts with improved selectivity.