Mechanism Of Dehydrogenation Research Articles

Nitrogen-phosphorus co-functionalized reduced graphene oxide supported NiCoPd-CeOx nanoparticles as a highly efficient and stable catalyst for formic acid dehydrogenation

Formic acid (HCOOH, FA), a common liquid hydrogen storage material, has attracted tremendous research interest. However, the development of efficient, low-cost and high-stable heterogeneous catalyst for selective dehydrogenation of FA remains a major challenge. In this paper, a simple co-reduction method is proposed to synthesize nitrogen-phosphorus co-functionalized rGO (NPG) supported ultrafine NiCoPd-CeO x nanoparticles (NPs) with a mean size of 1.2 nm. Remarkably, the as-prepared Ni 0.2 Co 0.2 Pd 0.6 -CeO x /NPG shows outstanding catalytic activity for FA dehydrogenation, affording a high TOF value of 6506.8 mol H 2 mol Pd −1 h −1 at 303 K and a low activation energy of 17.7 kJ mol −1 , which is better than most of the reported heterogeneous catalysts, and can be ascribed to the combined effect of well-dispersed ultrafine NiCoPd-CeO x NPs, modified Pd electronic structure, and abundant active sites. The reaction mechanism of dehydrogenation of FA is also discussed. Furthermore, the optimized Ni 0.2 Co 0.2 Pd 0.6 -CeO x /NPG shows excellent stability over 10 th run with 100% conversion and 100% H 2 selectivity, which may provide more possibilities for practical application of FA system on fuel cells. • N–P co-functionalized rGO supported ultrafine NiCoPd-CeO x NPs are successfully synthesized via a simple co-reduction method. • NPG has a positive effect on improving the distribution and controlling particle size. • The Ni 0.2 Co 0.2 Pd 0.6 -CeO x /NPG exhibits high activity towards FA dehydrogenation, giving a TOF of 6506.8 h −1 at 303 K. • The Ni 0.2 Co 0.2 Pd 0.6 -CeO x /NPG shows excellent stability and activity even after 10 th run.

Mechanism and Kinetics of n-Butane Dehydrogenation to 1,3-Butadiene Catalyzed by Isolated Pt Sites Grafted onto ≡SiOZn–OH Nests in Dealuminated Zeolite Beta

An interest in the on-purpose production of 1,3-butadiene (1,3-BD) has grown, as a consequence of the decline in naphtha cracking for the production of ethene and propene, products that can now be produced economically by thermal dehydrogenation of ethane and propane contained in natural gas. In this study, the mechanism and kinetics of n-butane dehydrogenation to 1,3-BD are explored over atomically distributed Pt sites grafted onto dealuminated zeolite BEA (DeAlBEA) in the form of (≡Si–O–Zn)4–6Pt complexes. Reaction of n-butane dehydrogenation carried out at 823 K with 2.53 kPa n-butane/He and a weight-hourly space velocity (WHSV) of 14.5 h–1 produced 1,3-BD with a turnover frequency of 0.45 mol 1,3-BD (mol Pt)−1 s–1. Space-time studies and identification of the reaction intermediates suggest that n-butane first undergoes dehydrogenation primarily to 1-butene, which then rapidly isomerizes to produce an equilibrated mixture of 1-butene and 2-butene. 1-Butene then undergoes secondary dehydrogenation to produce 1,3-BD. We report, here, a detailed study of the kinetics of n-butane dehydrogenation to butenes and 1-butene dehydrogenation to 1,3-BD over isolated Pt sites. Both reactions exhibit a Langmuir–Hinshelwood dependence on n-butane and 1-butene partial pressures, respectively. Comparison of effective forward rate constants of n-butane dehydrogenation to butenes (k1f) and butene dehydrogenation to 1,3-BD (k2f) shows that the isolated Pt sites grafted onto DeAlBEA exhibit a very high activity for sequential dehydrogenation of n-butane to 1,3-BD relative to other Pt-based catalysts previously reported.

Mechanism of complete dehydrogenation of ammonia borane in electrochemical alkaline environment

Ammonia borane (NH3BH3, AB) has been considered to be a promising chemical hydrogen storage material. The dehydrogenation reaction of AB on the surface of MgSiP2 is investigated by the first-principles method. We have verified the two conventional intramolecular dehydrogenation pathways in the AB hydrolysis reaction, B-distal dehydrogenation (the rate-determining step (RDS) was 0.71 eV) and B-N bond dissociation dehydrogenation (the RDS was 1.00 eV). A new reaction route for dehydrogenation, the BN alternate dehydrogenation, was also explored. The reaction heat of the RDS was 0.71 eV. Note that the entire reaction process in the path of the dissociation of the BN bond can completely release the 6H protons in AB. With the help of the dissociation of H2O, the H2 output ratio of 1:6 can be achieved. In addition, we also considered the influence of *OH– on the RDS of each dehydrogenation reaction in alkaline environment. The calculations have found that the presence of *OH– is beneficial to reduce the reaction heat of dehydrogenation in the AB hydrolysis reaction, making the reaction heat of the RDS of B-distal dehydrogenation is changed from 0.71 eV to 0.15 eV, the B-N bond dissociation dehydrogenation is changed from 1.00 eV to 0.09 eV and the BN alternate dehydrogenation is changed from 0.71 eV to 0.15 eV. This shows that *OH– greatly promotes the production of H2 from the dehydrogenation of AB.

Theoretical investigation of the hydrogen production by adsorption of methanol on bimetallic Pd-Ge (1 1 0) surface as future green combustible using DFT-D method: Energetic and structural aspect of interaction pathways of metal with methanol

Dehydrogenation and adsorption mechanism of methanol on PdGe (110) surface was undertaken using self-consistent periodic DFT-D. Different kinds of adsorption modes of relevant intermediates on the surface were identified. It was found that methanol and CHO prefer to adsorb on top site(tPd), CH3O, CH2OH adsorb on top(tGe), while CHOH, COH, CO, and H adsorb on bridge(bPdPd) and CH2O on top(tPd; tGe) sites. The four-way reactions indicated that the initial OH bond scission of methanol seems to be more favorable than CH bond cleavage on PdGe (110) from the perspective of activation barriers. It is also shown that (CH3OH → CH3O → CH2O → CHO → CO) is the predominant pathway on PdGe (110). Ge Insertion in Pd(110) shows that the predominant path is different from those of Pd(100), Pd(111), also the activation barrier of PdGe (110) is lower than those of Pd(100), Pd(111).

The curious saga of dehydrogenation/hydrogenation for chemical hydrogen storage: a mechanistic perspective.

Hydrogen storage is an indispensable component of hydrogen-based fuel economy. Chemical hydrogen storage relies on the development of lightweight compounds which can deliver high weight percentage of H2 at moderate temperatures through dehydrogenation and can be recovered from the dehydrogenated mass by hydrogenation for reuse. In this feature article we primarily discuss the mechanistic underpinnings of the catalytic dehydrogenation of ammonia-borane, a potential candidate for hydrogen storage and the challenges associated with its regeneration from the dehydrogenated mass. Moreover, we highlight the mechanistic intricacies, viability, sustainability and unresolved issues of allied chemical hydrogen storage avenues such as the CH3OH-CO2 cycle.

Theoretical Insight into the Reaction Mechanism of Ammonia Dehydrogenation on Iron-Based Clusters

Theoretical Insight into the Reaction Mechanism of Ammonia Dehydrogenation on Iron-Based Clusters

First principle study of adsorption and desorption behaviors of NH<sub>3</sub> molecule on the TaC (0001) surface

The adsorption and desorption behaviors of ammonia on TaC(0001) surface are studied by employing spin-polarized density function theory calculations. The surface energy calculation results show that the TaC (0001) terminating with Ta is the most stable surface. According to the optimized structural and energetic properties, it is found that NH<sub>3</sub> prefers to adsorb on the top site, whereas NH<sub>2</sub>, H prefer to adsorb on the triple hcp site and NH, N prefer to stay on the triple fcc site. In addition, three transition states are found for analyzing the mechanism of dehydrogenation of NH<sub>3</sub>, and the N recombination reaction is also considered. The results show that the desorption of nitrogen atoms is the rate-determining step in the overall reaction. Finally, in order to further elucidate the mechanism of NH<sub>3</sub> adsorption and dissociation on the surface of Ta-TaC, the electronic structure of the most stable adsorption position is analyzed from the perspective of charge density distribution and electron density of states. The results of electronic structure calculation show that NH<sub>3</sub> molecule is adsorbed on the surface through the mixture of 2p<i><sub>z</sub></i> orbital of N atom and <inline-formula><tex-math id="Z-20211229103116-1">\begin{document}$ 5{\rm d}_{z^2} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20210400_Z-20211229103116-1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="1-20210400_Z-20211229103116-1.png"/></alternatives></inline-formula> orbital of substrate Ta. With the progress of dehydrogenation, the charge transfer phenomenon becomes more and more serious. The charge transfer between adsorbate and substrate plays an important role in accelerating NH<sub>3</sub> dehydrogenation catalytic process.

Solvent-free synthesis of Rh/meso-Al2O3 via mechanochemistry for hydrolytic dehydrogenation of ammonia borane

An effective strategy synthesis of Rh/meso-Al2O3 catalysts was demonstrated by mechanochemistry for hydrolytic dehydrogenation of ammonia borane (AB). These catalysts are characterized systematically by N2 adsorption-desorption isotherms, X-ray diffraction (XRD), X-ray photoelectron spectrometry (XPS), scanning electron microscope (SEM), and transmission electron microscope (TEM). The results show that the turnover frequency (TOF) and activation energy (Ea) are 246.8 molH2·molRh−1·min−1 and 47.9 kJ mol−1 for hydrolytic dehydrogenation of at 298 K catalyzed by Rh/Al2O3-CTAB-400, obviously higher than those previously reported catalysts. Furthermore, catalyst Rh/Al2O3-CTAB-400 can be recycled by simple centrifugal separation and the catalytic activity is still well maintained after five cycles. In addition, a plausible mechanism for hydrolytic dehydrogenation of AB has also been proposed. This mechanochemical synthesis method exhibits great application prospects for the preparation of heterogeneous catalysts.

Mechanisms of hydrides’ nucleation and the effect of hydrogen pressure induced driving force on de-/hydrogenation kinetics of Mg-based nanocrystalline alloys

Aiming to gain insight on the hydrogen storage properties of Mg-based alloys, partial hydrogenation and hydrogen pressure related de-/hydrogenation kinetics of Mg–Ni–La alloys have been investigated. The results indicate that the phase boundaries, such as Mg/Mg2Ni and Mg/Mg17La2, distributed within the eutectics can act as preferential nucleation sites for β-MgH2 and apparently promote the hydrogenation process. For bulk alloy, it is observed that the hydrogenation region gradually grows from the fine Mg–Ni–La eutectic to primary Mg region with the extension of reaction time. After high-energy ball milling, the nanocrystalline powders with crystallite size of 12∼20 nm exhibit ameliorated hydrogen absorption/desorption performance, which can absorb 2.58 wt% H2 at 368 K within 50 min and begin to desorb hydrogen from ∼508 K. On the other side, variation of hydrogen pressure induced driving force significantly affects the reaction kinetics. As the hydrogenation/dehydrogenation driving forces increase, the hydrogen absorption/desorption kinetics is markedly accelerated. The dehydrogenation mechanisms have also been revealed by fitting different theoretical kinetics models, which demonstrate that the rate-limiting steps change obviously with the variation of driving forces.

DFT Probe into the Mechanism of Formic Acid Dehydrogenation Catalyzed by Cp*Co, Cp*Rh, and Cp*Ir Catalysts with 4,4'-Amino-/Alkylamino-Functionalized 2,2'-Bipyridine Ligands.

The mechanistic landscape of H2 generation from formic acid catalyzed by Cp*M(III) complexes (M = Co or Rh or Ir) with diamino-/dialkylamino-substituted 2,2'-bipyridine ligand architectures have been unveiled computationally. The calculations indicate that the β-hydride elimination process is the rate-determining step for all the investigated catalysts. The dialkylamino moieties on the 2,2'-bipyridine ligand were found to reduce the activation free energy required for the rate-limiting β-hydride elimination step and increase the hydridic nature of the Ir-hydride bond, which accounts for the experimentally observed enhanced catalytic activity. Furthermore, the protonation by H3O+ ion was found to be the kinetically most favorable route than the conventional protonation by formic acid. The origin for this preference lies in the increased electrophilicity of the proton from hydronium ion which facilitates easy protonation of the metal-hydride with low activation energy barrier. The Co and Rh analogues of the chosen iridium catalyst were computationally designed and were estimated to possess a rate-determining activation barrier of 16.9 and 14.5 kcal/mol, respectively. This illustrates that these catalysts are potential candidates for FAD. The insights derived in this work might serve as a vital knowledge that could be capitalized upon for designing cost-effective catalyst for FAD in future.

Structural Characterization of Nickel-Doped Aluminum Oxide Cations by Cryogenic Ion Trap Vibrational Spectroscopy.

Isolated nickel-doped aluminum oxide cations (NiOm)(Al2O3)n(AlO)+ with m = 1-2 and n = 1-3 are investigated by infrared photodissociation (IRPD) spectroscopy in combination with density functional theory and the single-component artificial force-induced reaction method. IRPD spectra of the corresponding He-tagged cations are reported in the 400-1200 cm-1 spectral range and assigned based on a comparison to calculated harmonic IR spectra of low-energy isomers. Simulated spectra of the lowest energy structures generally match the experimental spectra, but multiple isomers may contribute to the spectra of the m = 2 series. The identified structures of the oxides (m = 1) correspond to inserting a Ni-O moiety into an Al-O bond of the corresponding (Al2O3)1-3(AlO)+ cluster, yielding either a doubly or triply coordinated Ni2+ center. The m = 2 clusters prefer similar structures in which the additional O atom either is incorporated into a peroxide unit, leaving the oxidation state of the Ni2+ atom unchanged, or forms a biradical comprising a terminal oxygen radical anion Al-O•- and a Ni3+ species. These clusters represent model systems for under-coordinated Ni sites in alumina-supported Ni catalysts and should prove helpful in disentangling the mechanism of selective oxidative dehydrogenation of alkanes by Ni-doped catalysts.

NMR used to study the side-reactions between peroxides and antioxidants during the reactive extrusion process of the impact polypropylene

Side reaction pathways are observed to occur between antioxidants and peroxide during the processing of multiple resin grades mediated by controlled peroxide-induced degradation of impact polypropylene. In the present work, the reaction mechanism and main by-products between antioxidants and peroxides were investigated. The results demonstrate that peroxides greatly accelerate the decomposition reactions, and the free radicals formed from peroxide decomposition react with, for example, the antioxidant AO1010 to produce dehydrogenation of phenyl propionic unit(s) at the α position (cinnamic acid ester moiety), which generates a conjugated system leading to the increased color of the product. It is the first time to confirm the cinnamic acid moiety's existence and report its NMR data. Further, this work confirms the dehydrogenation mechanism by comparison with different sterically hindered phenolic antioxidants. It also systematically summarizes the oxidation and degradation mechanism of AO168 and AO1010 under air and peroxide environments, respectively. Based on present study, clear guidelines are obtained to improve the quality of polymeric products, especially the appearance and stability, during product development.

Microwave plasma-based high temperature dehydrogenation of hydrocarbons and alcohols as a single route to highly efficient gas phase synthesis of freestanding graphene

Understanding underlying processes behind the simple and easily scalable graphene synthesis methods enables their large-scale deployment in the emerging energy storage and printable device applications. Microwave plasma decomposition of organic precursors forms a high-temperature environment, above 3000 K, where the process of catalyst-free dehydrogenation and consequent formation of C2 molecules leads to nucleation and growth of high-quality few-layer graphene (FLG). In this work, we show experimental evidence that a high-temperature environment with a gas mixture of H2 and acetylene, C2H2, leads to a transition from amorphous to highly crystalline material proving the suggested dehydrogenation mechanism. The overall conversion efficiency of carbon to FLG reached up to 47%, three times as much as for methane or ethanol, and increased with increasing microwave power (i.e. with the size of the high-temperature zone) and hydrocarbon flow rate. The yield decreased with decreasing C:H ratio while the best quality FLG (low D/G–0.5 and high 2D/G–1.5 Raman band ratio) was achieved for C:H ratio of 1:3. The structures contained less than 1 at% of oxygen. No additional hydrogen was necessary for the synthesis of FLG from higher alcohols having the same stoichiometry, 1-propanol and isopropanol, but the yield was lower, 15%, and dependent on the atom arrangement of the precursor. The prepared FLG nanopowder was analyzed by scanning electron microscopy, Raman, x-ray photoelectron spectroscopy, and thermogravimetry. Microwave plasma was monitored by optical emission spectroscopy.

Elucidation of active species and reaction mechanism of sulfide V-K/Al2O3 catalyst for isobutane dehydrogenation

Supported sulfide vanadium-based catalyst in dehydrogenation of light alkanes is becoming a promise to replace the commercial used Pt- and Cr-based catalysts, due to the lower cost and toxicity. Nonetheless, the nature of active sites and reaction mechanism for dehydrogenation of isobutane over sulfide vanadium-based catalysts are still ambiguous. In this study, a series of sulfide V-K/γ-Al2O3 catalysts were prepared, presenting diverse distribution of isolated, oligomeric and polymeric vanadium species on catalyst surface. The oligomeric species were demonstrated to be the active dehydrogenation sites, and the TOFoligo showed a closely correlation with the isobutane conversion. Besides, the dehydrogenation reaction mechanism was studied by in-situ DRIFTS. The results showed that isobutane would first dissociative adsorbed on catalyst surface, and the stable intermediates of vanadium-isobutenyl were detected. Furthermore, the deposited coke rather than sulfur loss was found to play the crucial role in deactivation. The vast majority of deposited coke existed as polyaromatic species and the other slight ones presented as aliphatic form. This study enriches the fundamental explorations in active sites and reaction mechanism of sulfide V-K/γ-Al2O3 catalysts during isobutane dehydrogenation, and provides an in-depth strategy to improve the activity and stability of vanadium-based dehydrogenation catalysts.

Unraveling the Mechanisms of Electrocatalytic Oxygenation and Dehydrogenation of Organic Molecules to Value‐Added Chemicals Over a Ni–Fe Oxide Catalyst

AbstractElectrocatalytic oxidative upgrading of organic molecules is a promising alternative process to water oxidation for clean hydrogen production. Yet, its underlying mechanism is still not fully understood, and suitable low‐cost electrocatalysts with good product selectivity and activity are still sought after. Here, an active NiFeOx‐based catalyst is reported on as a general platform for the electro‐oxidative upgrading of organic molecules through oxygenation and dehydrogenation, with hydrogen coproduction. Detailed mechanistic studies unveil that C–H bond oxidation (with a bond dissociation energy BDEC–H of ≈88–96 kcal mol−1) is involved in the rate‐limiting step, which differs significantly from the oxygen evolution reaction mechanism. These findings show that the oxidation efficacy is linearly correlated with the BDEC–H of the molecule. Thus, the catalyst can be used as a general platform for large‐scale electro‐oxidation of various substrates through oxygenation and dehydrogenation at high current density (25 mA cm−2), with a good Faradaic yield. The platform's generality is further demonstrated by the selective oxidation of 5‐(hydroxymethyl)furfural into 2,5‐furandicarboxylic acid with good efficiency.

Direct synthesis of p-methyl benzaldehyde from acetaldehyde via an organic amine-catalyzed dehydrogenation mechanism

Summaryp-Methyl benzaldehyde (p-MBA) is a class of key chemical intermediates of pharmaceuticals. Conventional industrial processes for p-MBA production involve the consecutive photochlorination, amination, and acid hydrolysis of petroleum-derived p-xylene, while producing vast pollutants and waste water. Herein, we report a direct, green route for selective synthesis of p-MBA from acetaldehyde using a diphenyl prolinol trimethylsilyl ether catalyst. The optimized p-MBA selectivity is up to 90% at an acetaldehyde conversion as high as 99.8%. Intermediate structure and 18O-isotope data revealed that the conversion of acetaldehyde to p-methylcyclohexadienal intermediates proceeds in an enamine-iminium intermediate mechanism. Then, controlled experiments and D-isotope results indicated that the dehydrogenation of p-methylcyclohexadienal to p-MBA and H2 is catalyzed by the same amines through an iminium intermediate. This is an example that metal-free amines catalyze the dehydrogenation (releasing H2), rather than using metals or stoichiometric oxidants.

Enhanced hydrogen storage properties of NaBH4–Mg(BH4)2 composites by NdF3 addition

As two important members of complex hydrides, Mg(BH4)2 and NaBH4 have a high gravimetric capacity (14.9 and 10.8 ​wt%, respectively). In this study, the Mg(BH4)2 was synthesized by the ion exchange method. Afterwards, the Mg(BH4)2 and NaBH4 composites with different amounts (30, 40 and 50 ​wt%) of NdF3 were prepared by mechanical milling. Effects of the NdF3 on the microstructural evolution and hydrogen storage properties were investigated. The results show that NdF3 catalyst can significantly improve the dehydrogenation kinetics of the eutectic composites of NaBH4–Mg(BH4)2. The onset hydrogen desorption temperature of the composites is about 88.6 ​°C, which is about 110 ​°C lower than that of Mg(BH4)2 and NaBH4 composites. Mg(BH4)2–NaBH4-0.5NdF3 composites can released 5.2 ​wt% H2 at 250 ​°C within 30 ​min, and the dehydrogenation capacity is significantly higher than that of Mg(BH4)2–NaBH4 composites. The analysis of the dehydrogenation mechanism reveals that NdF3 takes participate in the reaction to generate NaMgF3 to promote the dehydrogenation reaction process of the composites.

The mechanism of the water dissociation and dehydrogenation of glycerol on Au (111) and PdAu alloy catalyst surfaces

Hydrogen is an energy carrier found from renewable sources such as biomass, geothermal, solar, or wind. Water splitting and dehydrogenation of glycerol is a sustainable process of H2 production from renewables because water is abundant, and the glycerol is formed from the biomass-derived compounds. However, finding a suitable and best catalyst for these processes is challenging. Thus, this paper proposed a theoretical study to find the mechanism of the dissociation of water and dehydrogenation of glycerol using Au metal and PdAu alloy catalysts using the density functional theory (DFT) method. Four PdAu alloys have been constructed with different atomic compositions ranging from 1 to 3 of Pd metal to Au metal. The result showed strong adsorption on the Pd1Au3 catalyst surface, and the water splitting is best on the Pd3Au1 catalyst surface. Simultaneously, the glycerol adsorption on catalyst surfaces is tested before proceeding for the complete dehydrogenation mechanism of glycerol. Strong adsorption was found at the Pd1Au3 catalyst compared to other catalyst surfaces on the glycerol adsorption. The dehydrogenation mechanism was found toward a downhill reaction and removed eight hydrogens from the glycerol compared to Au metal, referring to easy dehydrogenation of glycerol using the alloy PdAu. The final species that adsorbed on the Pd1Au3 surface is the carbon monoxide will be turned later into carbon dioxide.

Dehydrogenation and dehydration of formic acid over orthorhombic molybdenum carbide

The dehydrogenation and dehydration of formic acid is investigated on the β-Mo2C (100) catalyst surface using time independent density functional theory. The energetics of the two mechanisms are calculated, and the thermochemistry and kinetics are discussed using the transition state theory. Subsequently, microkinetic modelling of the system is conducted, considering the batch reactor model. The potential energy landscape of the reaction shows a thermodynamically favourable cleavage of HCOOH to form CO; however, the kinetics show that the dehydrogenation mechanism is faster and CO2 is continuously formed. The effect of HCOOH adsorption on the surface is also analysed, in a temperature-programmed desorption, with the conversion proceeding at under 350 K and desorption of CO2 is observed with a selectivity of about 100 %, in line with the experimental reports.

Oxidative Dehydrogenation of 1-Butene to 1,3-Butadiene Over Metal Ferrite Catalysts

The oxidative dehydrogenation (ODH) of 1-butene to 1,3-butadiene was studied over a series of AFe2O4 catalysts, where A = Zn, Mn, Ni, Cu, Mg and Fe. The catalysts were characterised by XPS, EPR spectroscopy, BET surface area analysis, Raman spectroscopy and XRD. All the ferrites were active for ODH and gave an order of activity after 80 h on-stream of ZnFe2O4 > NiFe2O4 > MnFe2O4 > MgFe2O4 > CuFe2O4 > FeFe2O4. All catalysts lost significant surface area (up to ~ 80%) under reaction conditions of 0.75:1:15 oxygen:1-butene:steam with an overall GHSV of 10,050 h−1 at 693 K. Fe3O4 was unstable under reaction conditions and was converted to Fe2O3, which showed very low activity. Nickel ferrite was the only material that gave carbon dioxide as a significant product, all others were selective to 1,3-butadiene. Zinc ferrite gave a steady-state yield of 1,3-butadiene of ~ 80%. Inversion parameters were determined for the ferrites from XPS and a correlation was obtained between 1,3-butadiene yield and inversion parameter, indicating that Fe3+ in an octahedral hole is a key species in the mechanism of oxidative dehydrogenation. Butene isomerisation and ODH were shown to occur on different sites.