Projects / Programmes
Development of heterogeneous catalysts for oxidative dehydrogenation of propane with CO2
| Code |
Science |
Field |
Subfield |
| 7.00.00 |
Interdisciplinary research |
|
|
| Code |
Science |
Field |
| T350 |
Technological sciences |
Chemical technology and engineering |
| Code |
Science |
Field |
| 2.04 |
Engineering and Technology |
Chemical engineering
|
Propane, propylene, oxidative dehydrogenation, multifunctional redox catalyst, selectivity,activity, stability
Researchers (8)
Organisations (2)
Abstract
Alkanes are major constituents of natural gas and petroleum. However, there are very few processes for converting them directly to more valuable products due to their inertness and requirement of stringent reaction conditions.
Because it is difficult to achieve selective transformations under stringent reaction conditions, most important petrochemicals (especially oxygenates) are produced from much more reactive unsaturated hydrocarbons (olefins). As a result, a breakthrough in alkane chemistry could provide alternatives to current conversion pathways and thus significantly improve efficiency of their utilization. The goal of this research project is to develop an efficient strategy for direct catalytic conversion of alkanes to olefins, namely catalytic propane dehydrogenation to propylene using CO2 as a mild oxidant.
Presence of a heterogeneous catalyst significantly decreases the activation energy, required for C-H bond cleavage (from roughly 400 kJ/mol in non-catalyzed process to 50-150 kJ/mol in catalytic non-oxidative or oxidative dehydrogenation). This allows the reaction to proceed at lower temperatures. Proper design and tailoring of the catalyst enables some control of the transition states, resulting in better control over product selectivity.
In order to overcome the known issues of catalyst coking and propylene over-oxidation, an alternative pathway is proposed in this project: the use of a less powerful oxidant, namely CO2. Recent environmental and legislative trends encourage development of new reactions that use CO2 as a reactant.
To promote quick and efficient cleavage of the CO2 molecule (to extract the oxygen atom, which will participate as the active species in a cascade of elementary reaction steps during concerted C-H bond scission), a completely new class of catalysts will be developed. They will exhibit two types of adjacent active sites: (i) CeOx redox sites for CO2 disproportionation and (ii) VOx, MoOx, GaOx and WOx oligomeric clusters for oxidative activation and dehydrogenation of propane.
Close proximity of these two types of active sites is required in order to ensure fast relocation of oxygen species between site (i) and (ii), which will support the kinetically relevant step: oxidative propane activation.
Propane ODH catalysts will be based on thermally stable, high surface area mesoporous supports (CeO2-ZrO2, CeO2-Al2O3,…), which will be grafted with patches of type (ii) active sites. To construct required morphologies and achieve high dispersion of active sites, special attention will be focused to selection of appropriate precursors and solvents. Isoelectric point of the support and the use of support’s functional groups as grafting sites will also be considered during synthesis. To improve efficiency of CO2 disproportionation and propylene selectivity, alkali doping of the catalyst will be performed.
Establishing correlations between catalyst synthesis protocols, catalyst morphology and catalytic activity, selectivity and stability will be possible after performing catalytic tests in a plug flow reactor under a broad range of reaction conditions.
Catalytic activity of developed materials is expected to surpass the current state of the art propylene weight time yield of 2*10-4 mmol/gcatmin (0.5 g propylene/ gcath). The improvement will be enabled through careful tailoring and optimization of adjacent type (i) and (ii) active sites.
Characterization of developed catalysts will be performed using surface-sensitive and bulk; operando and ex-situ techniques such as DRIFTS, UV-Vis, Raman, EPR, XRD, H2-TPR, CO2-TPD… This information will enable thorough understanding of the catalyst, processes occurring on its surface, gas-solid interactions and analysis of the reaction mechanism.
Significance for science
The H2-TPR analysis showed different reactivity and quantity of labile lattice oxygen in the tested materials. Distinctly different steady-state and dynamic behavior of the tested catalysts was observed in the propane CO2-ODH reaction. Activity of CeO2 is stable, with low (15 %) propylene selectivity. Bulk CeVO4 shows no CO2 conversion; propylene is formed due to non-oxidative dehydrogenation. By increasing CeVO4 content from 10 to 20 wt. % in CeVO4/AC catalysts, both propane and CO2 conversions rise twofold. Over bulk V2O5 and CeVO4/AC catalysts, initial propylene selectivity was between 40-60 %. It drops to zero over V2O5 within 4 h of reaction, whereas remained almost stable for CeVO4/AC containing catalysts. Deactivation of bulk V2O5 and CeVO4/AC catalysts was observed with time on stream with concentrations of C3H6 and CO in the reactor discharge decreasing continuously. Contrary, concentrations of H2, CH4 and trace amounts of C2H4 were stable, indicating two parallel and independent reaction pathways: (i) propane CO2-ODH and (ii) non catalytic (thermal) propane cracking. In-situ DRIFT analysis revealed that activation of propane is associated with V2O5 and CeO2 lattice oxygen abstraction and catalyst reduction. Bulk CeVO4 does not react with C3H8. The CeO2 to a lesser extent, but CeVO4/AC and especially V2O5 suffer from very limited ability to activate CO2, therefore lattice O2- vacancy cannot be re-oxidized to close the catalytic cycle. Subsequently, this results in a progressive decline of their CO2-ODH activity. Absence of metallic clusters results in negligible accumulation of carbon on the catalyst, which is not the reason for observed deactivation. The research conducted in this project confirmed our initial hypothesis that the use of a soft oxidant (such as CO2) offers the benefits of higher propylene selectivity with less stringent active site architecture (compared to O2-ODH) and an additional chemical reaction for CO2 conversion. Bulk reducible oxides can perform the reaction with high selectivity and it is determined by the reactivity of lattice oxygen.
Significance for the country
Research activities covered in this application are based on an alternative and innovative approach to open up new pathways for environmentally friendly breakthrough technologies which can result in significantly increased recognition of the Laboratory for Environmental Sciences and Engineering at the National Institute of Chemistry in the global scale. Our activities are also expected to open new possibilities for closer cooperation with other Slovenian and foreign research institutions who share complimentary interests, as well as industrial companies active in hydrocarbon valorization. Also, the number of interested PhD students and post-doc researchers to work with scientists in our group is expected to increase. This will result in efficient knowledge transfer. Higher global recognition and high level of innovation and scientific excellence at the National Institute of Chemistry is expected to improve our efficiency in obtaining additional funding from the European fund Horizon2020, which will enable broadening and intensification of our research and ultimately its implementation through commercialization. The development of efficient processes for sustainable use of renewable resources and its transformation into chemicals and energy carriers which can be used on today's infrastructure could make a considerable contribution towards increasing the sustainable development and quality of living in Slovenia.
Most important scientific results
Final report
Most important socioeconomically and culturally relevant results
Final report
