Propane to olefins tandem catalysis: a selective route towards light olefins production

On-purpose synthetic routes for propylene production have emerged in the last couple of decades in response to the increasing demand for plastics and a shift to shale gas feedstocks for ethylene production. Propane dehydrogenation (PDH), an efficient and selective route to produce propylene, saw booming investments to fill the so-called propylene gap. In the coming years, however, a fluctuating light olefins market will call for flexibility in end-product of PDH plants. This can be achieved by combining PDH with propylene metathesis in a single step, propane to olefins (PTO), which allows production of mixtures of propylene, ethylene and butenes, which are important chemical building blocks for a.o. thermoplastics. The metathesis technology introduced by Phillips in the 1960s and mostly operated in reverse to produce propylene, is thus undergoing a renaissance of scientific and technological interest in the context of the PTO reaction. In this review, we will describe the state-of-the-art of PDH, propylene metathesis and PTO reactions, highlighting the open challenges and opportunities in the field. While the separate PDH and metathesis reactions have been extensively studied in the literature, understanding the whole PTO tandem-catalysis system will require new efforts in theoretical modelling and operando spectroscopy experiments, to gain mechanistic insights into the combined reactions and finally improve catalytic selectivity and stability for on-purpose olefins production.

Catalytic Dehydrogenation of Ethane: A Mini Review of Recent Advances and Perspective of Chemical Looping Technology

Dehydrogenation processes play an important role in the petrochemical industry. High selectivity towards olefins is usually hindered by numerous side reactions in a conventional cracking/pyrolysis technology. Herein, we show recent studies devoted to selective ethylene production via oxidative and non-oxidative reactions. This review summarizes the progress that has been achieved with ethane conversion in terms of the process effectivity. Briefly, steam cracking, catalytic dehydrogenation, oxidative dehydrogenation (with CO2/O2), membrane technology, and chemical looping are reviewed.

Catalytic conversion of ethane to valuable products through non-oxidative dehydrogenation and dehydroaromatization

Chemical utilization of ethane to produce valuable chemicals has become especially attractive since the expanded utilization of shale gas in the United States and associated petroleum gas in the Middle East. Catalytic conversion to ethylene and aromatic hydrocarbons through non-oxidative dehydrogenation and dehydroaromatization of ethane (EDH and EDA) are potentially beneficial technologies because of their high selectivity to products. The former represents an attractive alternative to conventional thermal cracking of ethane. The latter can produce valuable aromatic hydrocarbons from a cheap feedstock. Nevertheless, further progress in catalytic science and technology is indispensable to implement these processes beneficially. This review summarizes progress that has been achieved with non-oxidative EDH and EDA in terms of the nature of active sites and reaction mechanisms. Briefly, platinum-, chromium- and gallium-based catalysts have been introduced mainly for EDH, including effects of carbon dioxide co-feeding. Efforts to use EDA have emphasized zinc-modified MFI zeolite catalysts. Finally, some avenues for development of catalytic science and technology for ethane conversion are summarized.

Structural trends in the dehydrogenation selectivity of palladium alloys

Alloying is well-known to improve the dehydrogenation selectivity of pure metals, but there remains considerable debate about the structural and electronic features of alloy surfaces that give rise to this behavior. To provide molecular-level insights into these effects, a series of Pd intermetallic alloy catalysts with Zn, Ga, In, Fe and Mn promoter elements was synthesized, and the structures were determined using in situ X-ray absorption spectroscopy (XAS) and synchrotron X-ray diffraction (XRD). The alloys all showed propane dehydrogenation turnover rates 5–8 times higher than monometallic Pd and selectivity to propylene of over 90%. Moreover, among the synthesized alloys, Pd₃M alloy structures were less olefin selective than PdM alloys which were, in turn, almost 100% selective to propylene. This selectivity improvement was interpreted by changes in the DFT-calculated binding energies and activation energies for C–C and C–H bond activation, which are ultimately influenced by perturbation of the most stable adsorption site and changes to the d-band density of states. Furthermore, transition state analysis showed that the C–C bond breaking reactions require 4-fold ensemble sites, which are suggested to be required for non-selective, alkane hydrogenolysis reactions. These sites, which are not present on alloys with PdM structures, could be formed in the Pd₃M alloy through substitution of one M atom with Pd, and this effect is suggested to be partially responsible for their slightly lower selectivity.

Alloying is well-known to improve the dehydrogenation selectivity of pure metals, but there remains considerable debate about the structural and electronic features of alloy surfaces that give rise to this behavior.

Deactivation and regeneration of carbon supported Pt and Ru catalysts in aqueous phase hydrogenation of 2-pentanone

Aqueous phase conversion of biomass-derived molecules requires development of catalysts and operating strategies that create viable operation for extended performance as necessitated for industrial applications.