Kinetics of non-oxidative propane dehydrogenation on Cr2O3 and the nature of catalyst deactivation from first-principles simulations  

Autors: Matej Huš, Drejc Kopač, Blaž Likozar
Date: 03/03/2020

The paper evidences that non-oxidative dehydrogenation, although hitherto underutilised industrially, has been put forward as a viable and green alternative contributing in developing Circular Economy.

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Flux-Reducing Tendency of Pd-Based Membranes Employed in Butane Dehydrogenation Processes

Autors: by Thijs A. Peters*, Marit Stange and Rune Bredesen
Date: 16/10/2020

We report on the effect of butane and butylene on hydrogen permeation through thin state-of-the-art Pd–Ag alloy membranes. A wide range of operating conditions, such as temperature (200–450 °C) and H2/butylene (or butane) ratio (0.5–3), on the flux-reducing tendency were investigated.

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First-Principles-Based Multiscale Modelling of Nonoxidative Butane Dehydrogenation on Cr2O3(0001)

Autors: by Drejc Kopač, Damjan Lašič Jurković, Blaž Likozar and Matej Huš

Date: 10/12/2020

Propane and butane are short straight-chain alkane molecules that are difficult to convert catalytically. Analogous to propane, butane can be dehydrogenated to butenes (also known as butylenes) or butadiene, which are used industrially as raw materials when synthesizing various chemicals (plastics, rubbers, etc.).


In this study, we present results of detailed first-principles-based multiscale modelling of butane dehydrogenation, which can be paralleled to experimental data.
We found that among all the dehydrogenation products 2-butene (CH3CHCHCH3) is the most abundant product of dehydrogenation, with selectivity above 90%, concluding that the dehydrogenation of butane is a viable alternative to conventional olefin production processes.

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Ab Initio Multiscale Process Modeling of Ethane, Propane and Butane Dehydrogenation Reactions: A Review

Authors: Luka Skubic ,Julija Sovdat,Nika Teran,Matej Huš ,Drejc Kopač and Blaž Likozar

Date: 01/12/2020

Olefins are among the most important structural building blocks for a plethora of chemical reaction products, including petrochemicals, biomaterials and pharmaceuticals. An ever-increasing economic demand has urged scientists, engineers and industry to develop novel technical methods for the dehydrogenation of parent alkane molecules. In particular, the catalysis over precious metal or metal oxide catalysts has been put forward as an alternative way route to thermal-, steam- and fluid catalytic cracking (FCC).

In this review article, alkane dehydrogenation overview was presented in terms of multiscale modeling. We concentrated on ethane, propane, and butane dehydrogenation, presenting in a thorough manner the studies which focused on theoretical modeling. Theoretical understanding can often provide an insight into the catalyst nature, especially when the surface is decorated with metal dopants, or when the geometry is complex with steps, kinks, or different shapes. In such cases, in silico techniques can often provide order-of-magnitude estimates and trends that can be used to compare different materials, and to be used as a guide for the catalyst synthesis and the experimental setup.

The main conclusion is that for each alkane dehydrogenation process, there exist various catalysts, which show different performance. While Pt-based catalysts are most common among all processes, we find that other types are studied and provide different advancements in terms of cost, environmental issues, and/or catalytic performance such as selectivity, conversion, activity, degradation, etc. Another important aspect that we consider is whether the dehydrogenation process is oxidative or non-oxidative.

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Effect of Surface Oxidation on Oxidative Propane Dehydrogenation over Chromia: An Ab Initio Multiscale Kinetic Study

Matej Huš*, Drejc Kopač, David Bajec, and Blaž Likozar*

Date: 24/08/2021

An increasingly utilized way for the production of propene is propane dehydrogenation. The reaction presents an alternative to conventional processes based on petroleum resources. In this work, we investigate theoretically how Cr2O3 catalyzes this reaction in oxidative and reducing environments. Although previous studies showed that the reduced catalyst is selective for the non-oxidative dehydrogenation of propane, real operating conditions are oxidative. Herein, we use multiscale modeling to investigate the difference between the oxidized and reduced catalyst and their performance. The complete reaction pathway for propane dehydrogenation, including C–C cracking, formation of side products (propyne, ethane, ethylene, acetylene, and methane), and catalyst coking on oxidized and reduced surfaces of α-Cr2O3(0001), is calculated using density functional theory with the Hubbard correction. Parameters describing adsorption, desorption, and surface reactions are used in a kinetic Monte Carlo simulation, which employed industrially relevant conditions (700–900 K, pressures up to 2 bar, and varying oxidants: N2O, O2, and none). We observe that over the reduced surface, propene and hydrogen form with high selectivity. When oxidants are used, the surface is oxidized, which changes the reaction mechanism and kinetics. During a much faster reaction, H2O forms as a coproduct in a Mars–van Krevelen cycle. Additionally, CO2 is also formed, which represents waste and adversely affects the selectivity. It is shown that the oxidized surface is much more active but prone to the formation of CO2, while the reduced surface is less active but highly selective toward propene. Moreover, the effect of the oxidant used is investigated, showing that N2O is preferred to O2 due to higher selectivity and less catalyst coking. We show that there exists an optimum degree of surface oxidation, where the yield of propene is maximized. The coke, which forms during the reaction, can be burnt away as CO2 with oxygen.

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Effect of Surface Oxidation on Oxidative Propane Dehydrogenation over Chromia: An Ab Initio Multiscale Kinetic Study

Drejc Kopača ,Blaž Likozar ,Matej Huš

Date: 01/11/2021

Molecules that are difficult to convert catalytically often require a complex and specially tailored catalyst composition. Catalytic alkane dehydrogenation is an interesting example, where theoretical ab-initio and kinetic meso-scale simulations can provide the understanding of the performance improvement when the catalyst composition is altered. Herein, we study non-oxidative dehydrogenation of propane and butane over variously doped (Na, Li, K, Mg, Ca, or Cs) chromium oxide using first principles. The reaction pathway for the conversion of propane to propene/propyne and of butane to 1- and 2-butene is studied using density functional theory with the Hubbard U correction. Energies and kinetic parameters describing the adsorption, desorption, and surface reactions are used in mean-field microkinetic and kinetic Monte Carlo simulations. The process was modelled at industrially relevant temperatures, pressures, and feed gas flow velocities. Calculating the catalytic conversion, selectivity to products, and activity trends show that surface doping enhances the conversion and activity. The highest conversion for most dopants is achieved at temperatures below 850 K and atmospheric pressure, where the activity is significantly improved compared to the non-doped Cr2O3 catalyst.

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Pd-based membranes performance under hydrocarbon exposure for propane dehydrogenation processes: Experimental and modeling

C.Brencioa ,F.W.A.Fonteina ,J.A.Medranoa ,L.Di Felicea, A.Arratibelb , F.Gallucciac

Date: 01/11/2021

In this work, a novel Pd–Ag double-skinned (DS-) membrane is used for the first time in conditions typical of propane dehydrogenation (PDH). This membrane presents a protective layer on top of the H2-selective one, which acts as shield against chemical deactivation and mechanical erosion under reaction conditions. While the protective layer is already been proven as an efficient barrier against membrane erosion in fluidized beds, there is no validation yet under PDH reaction. The DS- membrane performance is compared with a conventional (C-) Pd–Ag membrane under alkane/alkene exposure, at 400–500 °C and 3 bar, to investigate whether the incorporation of the protective layer would be suited for H2 separation in PDH systems, and if coking rate would be affected. The novel membrane shows a H2 permeance of 2.28 × 10−6 mol∙m−2 s−1∙Pa−1 at 500 ᵒC and 4 bar of pressure difference, overcoming the performance of the conventional PdAg one (1.56x∙10−6 mol m−2 s−1∙Pa−1). Both membranes present a stable H2 flux under alkane exposure, while deactivation occurs under exposure to alkenes. A model able to describe the H2 flux through Pd-based membranes is presented to fit the experimental data and predict membrane performance. The model includes mass transfer limitations in the retentate and a corrective inhibition factor to account for the competitive adsorption of hydrocarbon species in the H2 selective layer. The experimental results obtained under alkene exposure deviates from model predictions; this can be attributed to carbon deposition on the surface of the selective layer, as further detected on the DS-membrane by Scanning Electron Microscopy (SEM)/Energy Dispersive X-Ray Analysis (EDX), which is the main factor for membrane deactivation.

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