Catalyst development for O2-assisted oxidative dehydrogenation of propane to propylene

O2-Assisted oxidative dehydrogenation of propane (O2-ODHP) could convert abundant shale gas into propylene as an important chemical raw material, meaning O2-ODHP has practical significance. Thermodynamically, high temperature is beneficial for O2-ODHP; however, high reaction temperature always causes the overoxidation of propylene, leading to a decline in its selectivity. In this regard, it is crucial to achieve low temperatures while maintaining high efficiency and selectivity during O2-ODHP. The use of catalytic technology provides more opportunities for achieving high-efficiency O2-ODHP under mild conditions. Up to now, many kinds of catalytic systems have been elaborately designed, including transition metal oxide catalysts (such as vanadium-based catalysts, molybdenum-based catalysts, etc.), transition metal-based catalysts (such as Pt nanoclusters), rare earth metal oxide catalysts (especially CeO2 related catalysts), and non-metallic catalysts (BN, other B-containing catalysts, and C-based catalysts). In this review, we have summarized the development progress of mainstream catalysts in O2-ODHP, aiming at providing a clear picture to the catalysis community and advancing this research field further.

Coupling acid catalysis and selective oxidation over MoO3-Fe2O3 for chemical looping oxidative dehydrogenation of propane

Redox catalysts play a vital role in chemical looping oxidative dehydrogenation processes, which have recently been considered to be a promising prospect for propylene production. This work describes the coupling of surface acid catalysis and selective oxidation from lattice oxygen over MoO₃-Fe₂O₃ redox catalysts for promoted propylene production. Atomically dispersed Mo species over γ-Fe₂O₃ introduce effective acid sites for the promotion of propane conversion. In addition, Mo could also regulate the lattice oxygen activity, which makes the oxygen species from the reduction of γ-Fe₂O₃ to Fe₃O₄ contribute to selectively oxidative dehydrogenation instead of over-oxidation in pristine γ-Fe₂O₃. The enhanced surface acidity, coupled with proper lattice oxygen activity, leads to a higher surface reaction rate and moderate oxygen diffusion rate. Consequently, this coupling strategy achieves a robust performance with 49% of propane conversion and 90% of propylene selectivity for at least 300 redox cycles and ultimately demonstrates a potential design strategy for more advanced redox catalysts.

Compositional dependence of Co- and Mo-supported beta zeolite for selective one-step hydrotreatment of methyl palmitate to produce bio jet fuel range hydrocarbons

For producing a drop-in bio jet fuel, one-step hydrotreatment, which includes deoxygenation, isomerization and cracking in one step, is essential to overcome the typical biofuel drawbacks due to high oxygen content, out of jet fuel range hydrocarbons, and low isomerization degree. Herein, Co- or/and Mo-supported Beta(25) zeolites with various Co/Mo ratios were prepared as transition metal-supported zeolite catalysts without the need for sulfidation of conventional transition metal catalysts. Based on the catalyst characterization, the Co/Mo ratio alters the metal phase with the appearance of CoMoO₄ and the altered Co metal phase strongly influences the acidic properties of Beta(25) by the formation of Lewis (L) acid sites with different strengths as Co₃O₄ and CoMoO₄ for strong and weak L acid sites, respectively. The catalytic activities were investigated for hydrotreatment of methyl palmitate as a biofuel model compound of fatty acid methyl esters. Primarily, Co is required for deoxygenation and Mo suppresses overcracking to enhance the yield of jet fuel range hydrocarbons. The Co/Mo ratio plays an important role to improve the C₈-C₁₆ selectivity by modifying the acidic properties to inhibit excessive cracking. Co₅Mo₁₀/Beta(25) achieved the best catalytic performance with the conversion of 94.2%, C₈-C₁₆ selectivity of 89.7 wt%, and high isomer ratio of 83.8% in organic liquid product. This unique modification of acidic properties will find use in the design of optimal transition metal-supported zeolite catalysts for selective one-step hydrotreatment to produce bio jet fuel range hydrocarbons.

Thermal-Driven Optimization of the Strong Metal-Support Interaction of a Platinum-Manganese Oxide Octahedral Molecular Sieve to Promote Toluene Oxidation: Effect of the Interface Pt2+-Ov-Mnδ. ACS APPLIED MATERIALS & INTERFACES 2022;14:56790-56800. [PMID: 36524882 DOI: 10.1021/acsami.2c16923] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Strong metal-support interactions (SMSIs) have a significant effect on the performance of supported noble-metal catalysts for volatile organic compound (VOC) elimination. Herein, the strength of the SMSI of Pt/OMS-2 between Pt and the OMS-2 support is regulated by simply changing calcination temperatures, and the catalyst calcined at 300 °C (Pt/OMS-2-300) performs the best in the catalytic combustion of toluene. Through systematic structural characterizations, it is revealed that much more Pt²⁺-O_v-Mn^δ+ species are formed in Pt/OMS-2-300, which can help facilitate the generation of more reactive oxygen species and promote lattice oxygen mobility. Moreover, the results of in situ DRIFTS experiments further confirm that abundant Pt²⁺-O_v-Mn^δ+ species at the Pt-MnO₂ interface on Pt/OMS-2-300 can better enhance the adsorption and activation of toluene, thus boosting the catalytic performance in toluene combustion. This newly developed strategy of thermal-driven regulation of the SMSI provides a novel perspective for constructing highly efficient catalysts for VOC emission control.

Boron nitride materials as emerging catalysts for oxidative dehydrogenation of light alkanes

Light olefins (C₂-C₄) play a crucial role as basic ingredients in chemical industry, and oxidative dehydrogenation (ODH) of light alkanes to olefins has been one of the popular routes since the shale gas revolution. ODH of light alkanes has advantages on energy-and-cost saving as compared with traditional direct dehydrogenation, but it is restricted by its overoxidation which results in the relatively low olefin selectivity. Boron nitride (BN), an interesting nanomaterial with an analogous structure to graphene, springs out and manifests the superior performance as advanced catalysts in ODH, greatly improving the olefin selectivity under high alkane conversion. In this review, we introduce BN nanomaterials in four dimensions together with typical methods of syntheses. Traditional catalysts for ODH are also referred as comparison on several indicators-olefin yields and preparation techniques, including the metal-based catalysts and the non-metal-based catalysts. We also surveyed the BN catalysts for ODH reaction in recent five years, focusing on the different dimensions of BN together with the synthetic routes accounting for the active sites and the catalytic ability. Finally, an outlook of the potential promotion on the design of BN-based catalysts and the possible routes for the exploration of BN-related catalytic mechanisms are proposed.

Effect of MnO2 Polymorphs' Structure on Low-Temperature Catalytic Oxidation: Crystalline Controlled Oxygen Vacancy Formation

MnO₂ polymorphs (α-, β-, and ε-MnO₂) were synthesized, and their chemical/physical properties for CO oxidation were systematically studied using multiple techniques. Density functional theory (DFT) calculations and temperature-programmed experiments reveal that β-MnO₂ shows low energies for oxygen vacancy generation and excellent redox properties, exhibiting significant CO oxidation activity (T₉₀ = 75 °C) and stability even under a humid atmosphere. For the first time, we report that the specific reaction rate for β-MnO₂ (0.135 molecule_CO·nm^-2·s^-1 at 90 °C) is roughly approximately 4 and 17 times higher than that of ε-MnO₂ and α-MnO₂, respectively. The specific reaction rate order (β-MnO₂ > ε-MnO₂ > α-MnO₂) is not only in good agreement with reduction rates (CO-TPSR measurements) but also agrees with the DFT calculation. In combination with in situ spectra and intrinsic kinetic studies, the mechanisms of CO oxidation over various crystal structures of MnO₂ were proposed as well. We believe the new insights from this study will largely inspire the design of such a kind of catalyst.

Interactions between CO oxidation and selective catalytic reduction of NO with NH3 over Mn-based catalysts

The α-MnO2-Cu catalyst has a high NO and CO removal rate. CO reduced the NH3-SCR activity by inhibiting NO adsorption. NH3 negatively affected CO oxidation by minimizing the formate intermediate. NO decomposed intermediates to promote CO oxidation.

Molybdenum Oxide Clusters: Structure, Stability, and Electronic Properties

Ab initio calculations were carried out to understand the structural, electronic, and energetic properties of molybdenum oxide clusters, Mo_mO_n (m = 1-6; n = 1-3m), to understand the relationships between size, composition, and reactivity. In clusters with a low oxygen-to-molybdenum ratio, there are bridge-bonded and linearly bonded oxygen atoms on a molybdenum core, while at higher ratios, Mo atoms are separated from each other and oxygen atoms located between the molybdenum atoms. The energy gap between the highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs) widens with n, i.e., at a high oxygen-to-molybdenum ratio. Stoichiometric Mo_mO_3m clusters (m > 1) have a HOMO-LUMO gap that ranges from 2.6 to 3.4 eV in neutral conditions and less than 0.6 eV in ionic states. The ionization potential of Mo_mO_3m clusters is higher than 10 eV. Mo_mO_n clusters qualitatively and quantitatively exhibit a similar electronic structure to the bulk. The energy of the reduction reaction, Mo_mO_n → Mo_mO_n-1 + 1/2O₂, is on average lower in clusters with high oxygen content; for example, the reduction energies of Mo₆O₁₈ and Mo₆O₉ are 2.23 and 5.19 eV, respectively. In the fragmentation of Mo_mO_n clusters, the general trend for clusters with a low oxygen-to-molybdenum ratio is the separation of a Mo atom or a Mo₂ dimer from the cluster, while clusters with higher oxygen content mostly form stoichiometric MoO₃, Mo₂O₆, and Mo₃O₉ clusters.

Laser-Induced MoOx/Sulfur-Doped Graphene Hybrid Frameworks as Efficient Antibacterial Agents

Rational design and scalable construction of antibacterial mediators based on unique graphene architectures with highly efficient antibacterial ability and significant biocompatibility are challenging. Herein, sulfur-doped graphene skeletons uniformly decorated with metal oxide nanoparticles were designed and constructed via one-step laser-induced microexplosive techniques and demonstrated for the first time as highly efficient antibacterial agents. The optical density and flat colony counting methods demonstrated that the as-designed laser-induced MoO_x/sulfur-doped graphene hybrids exhibited exceptional activity inhibition of Escherichia coli and Staphylococcus aureus. Moreover, the bacteria were treated with an impressive laser-induced MoO_x/sulfur-doped graphene colloidal solution of concentration as low as 1 mg/mL for 4 h, leading to an excellent viability loss of 85% for the two bacteria. Cell toxicity experiments proved that the biological toxicity of laser-induced MoO_x/sulfur-doped graphene to pig sperm cells was negligible. The molecular dynamics calculations proposed that the intrinsic interaction with N-acetylglucosamine at the cell wall and the high-efficiency synergistic effect of sulfur-doped graphene and MoO_x played the key role in inhibiting the viability of bacteria. This work provides new insights for a novel structure design and opens up a potential route to construct antibacterial agents with high efficiency for clinical application.

Elucidating the nature of Mo species on ZSM-5 and its role in the methane aromatization reaction

The valorization of methane is one of the most important goals during the transition period to the general use of renewable energies.

Plasma-enhanced direct conversion of CO2 to CO over oxygen-deficient Mo-doped CeO2

Plasma CO2 splitting to CO over oxygen-deficient Mo-doped CeO2 under mild conditions was investigated for the first time, showing ∼20 times higher CO2 conversion compared to pure CeO2, which can be attributed to the increased oxygen vacancies (VO) and the formation of Ce3+-VO-Mo on the catalyst surface. Importantly, VO sites showed excellent catalytic stability.

Structure analysis of supported disordered molybdenum oxides using pair distribution function analysis and automated cluster modelling

Molybdenum oxides and sulfides on various low-cost high-surface-area supports are excellent catalysts for several industrially relevant reactions. The surface layer structure of these materials is, however, difficult to characterize due to small and disordered MoO x domains. Here, it is shown how X-ray total scattering can be applied to gain insights into the structure through differential pair distribution function (d-PDF) analysis, where the scattering signal from the support material is subtracted to obtain structural information on the supported structure. MoO x catalysts supported on alumina nanoparticles and on zeolites are investigated, and it is shown that the structure of the hydrated molybdenum oxide layer is closely related to that of disordered and polydisperse polyoxometalates. By analysing the PDFs with a large number of automatically generated cluster structures, which are constructed in an iterative manner from known polyoxometalate clusters, information is derived on the structural motifs in supported MoO x .

MoO3/Al2O3 catalysts for chemical-looping oxidative dehydrogenation of ethane

MoO₃/γ-Al₂O₃ catalysts containing 0.3-3 monolayer (ML) equivalents of MoO₃ were prepared, characterized, and tested for ethane oxidative dehydrogenation (ODH) in cyclic redox and co-feed modes. Submonolayer catalysts contain highly dispersed (2D) polymolybdate structures; a complete monolayer and bulk Al₂(MoO₄)₃ are present at >1ML loadings. High ethylene selectivity (>90%) in chemical looping (CL) ODH correlates with Mo^+VI to Mo^+V reduction; CO_x selectivity is <10% under these conditions. Mo^+V and Mo^+IV species trigger CH₄ production resulting in much higher conversion albeit with <20% selectivity. In CL-ODH, submonolayer catalysts exhibit ethylene selectivities that decrease linearly from 96% at near-zero conversion to 70% at 45% conversion. >1ML catalysts provide higher conversions albeit with 10%-18% lower selectivity and greater selectivity loss with increasing conversion. In co-feed mode, ethylene selectivity drops to <50% at 46% conversion for a 0.6ML catalyst, but selectivity is virtually unaltered for a 3ML catalyst. We infer that at <1ML loadings, small domain size and strong Mo-O-Al bonds decrease 2D polymolybdate reducibility and enhance ethylene selectivity in CL-ODH.

Boron-hyperdoped silicon for the selective oxidative dehydrogenation of propane to propylene

Boron-hyperdoped silicon with enriched surface BO_x and B–OH species showed enhanced propylene productivity in the oxidative dehydrogenation of propane.

Understanding trends in methane oxidation to formaldehyde: statistical analysis of literature data and based hereon experiments

A regression tree analysis on selective oxidation of methane to methanol/formaldehyde was applied to identify fundamentals affecting catalyst performance. The electronegativity correlates with methane activation energy and formaldehyde selectivity.

Oxidation of acetone over Co-based catalysts derived from hierarchical layer hydrotalcite: Influence of Co/Al molar ratios and calcination temperatures

In order to enhance catalytic performance for acetone, Co-based catalysts prepared under different Co/Al molar ratios and calcination temperatures have been studied in this work. The results indicated that the catalytic activities of the catalysts firstly increased and then decreased with the increase of the Co/Al molar ratio and decreased with the increase of the calcination temperature. Based on the catalytic activities, TG/DTA, XRD, TPR and XPS characterization results, it can be found that catalytic activities of the catalysts with various Co/Al molar ratios were effected by the good crystallization structure of catalyst precursor, surface Co³⁺/Co²⁺ molar ratio, low temperature reducibility, and O_ads/O_latt molar ratio of the catalysts. Meanwhile, the catalytic activities of the catalysts with different calcination temperatures depended on the low temperature reducibility, surface Co³⁺/Co²⁺ molar ratio, porous structure and crystallization structure of the catalyst. Among different synthetic composition, 5:1 CoAlO-300 catalyst (T_90% = 225 °C) and 5:1 CoAlO-200 catalyst (T_90% = 222 °C) exhibited the efficient acetone oxidation.

Oxidative dehydrogenation of propane over Pt–Sn/Si-beta catalysts: key role of Pt–Sn interaction

Bimetallic Pt–Sn catalysts supported on dealuminated Si-beta zeolite were prepared via wet impregnation and the nanoscale close contact between Pt and Sn species in Pt–Sn/Si-beta was confirmed by electron microscopy analyses.

Experimental characterization of enhanced SNCR process with carbonaceous gas additives

Carbonaceous gases such as CO and alkanes are commonly used as additives to enhance the selective non-catalytic reduction (SNCR) performance due to their high reducibility. This study compared the effect of CO and CH₄ on NO reduction in a tubular reactor with simulated flue gas. The enhancement of C₃H₈ on SNCR process was tested at extremely low temperature, i.e. 650 °C. Experimental results suggested that reactions between NH₃ and SO₂ were favored at low temperatures and the competition for NH₃ between SO₂ and NO was influenced by gas additives. A maximum downward shift of 25 °C and 100 °C in temperature window for 50% NO reduction efficiency was obtained with the addition of CO and CH₄, respectively. Considerable CO emission was observed with addition of CH₄. The addition of CH₄ contributed to the formation of a self-accelerating reaction route within NO/O₂/NH₃ SNCR reaction system. NO₂ produced from NO accelerates the oxidation of CH₄ to CO, while the oxidation of CH₄ returns to enhance the NO reduction globally. Optimal NO reduction of 44% was achieved with addition of C₃H₈ at 650 °C. Substantial portion of C₃H₈ was partially oxidized to CO and the remaining was converted into C₂H₄ and C₃H₆ during the SNCR process. Oxidative dehydrogenation of C₃H₈ was involved. High reactivity of C₃H₆ and C₂H₄ favored the further oxidation and cracking to produce CO. These differences in oxidation behavior significantly influence the promotion capacities of CO, CH₄ and C₃H₈ for NO reduction.