B2O3@BPO4 sandwich-like hollow spheres as metal-free supported liquid-phase catalysts

Surface Chemistry and Catalytic Reactivity of Borocarbonitride in Oxidative Dehydrogenation of Propane

Borocarbonitride (BCN) materials are newly developed oxidative dehydrogenation catalysts that can efficiently convert alkanes to alkenes. However, BCN materials tend to form bulky B2 O3 due to over-oxidation at the high reaction temperature, resulting in significant deactivation. Here, we report a series of super stable BCN nanosheets for the oxidative dehydrogenation of propane (ODHP) reaction. The catalytic performance of the BCN nanosheets can be easily regulated by changing the guanine dosage. The control experiment and structural characterization indicate that the introduction of a suitable amount of carbon could prevent the formation of excessive B2 O3 from BCN materials and maintain the 2D skeleton at a high temperature of 520 °C. The best-performing catalyst BCN exhibits 81.9 % selectivity towards olefins with a stable propane conversion of 35.8 %, and the propene productivity reaches 16.2 mmol h-1  g-1 , which is much better than hexagonal BN (h-BN) catalysts. Density functional theory calculation results show that the presence of dispersed rather than aggregated carbon atoms can significantly affect the electronic microenvironment of h-BN, thereby boosting the catalytic activity of BCN.

Multiple Promotional Effects of Vanadium Oxide on Boron Nitride for Oxidative Dehydrogenation of Propane

Featuring high olefin selectivity, hexagonal boron nitride (h-BN) has emerged recently as an attractive catalyst for oxidative dehydrogenation of propane (ODHP). Herein, we report that dispersion of vanadium oxide onto BN facilitates the oxyfunctionalization of BN to generate more BO _x active sites to catalyze ODHP via the Eley-Rideal mechanism and concurrently produce nitric oxide to initiate additional gas-phase radical chemistry and to introduce redox VO _x sites to catalyze ODHP via the Mars-van Krevelen mechanism, all of which promote the catalytic performance of BN for ODHP. As a result, loading 0.5 wt % V onto BN has doubled the yield of light alkene (C₂-C₃) at 540-580 °C, and adding an appropriate concentration of NO in the reactants further enhances the catalytic performance. These results provide a potential strategy for developing efficient h-BN-based catalysts through coupling gas-phase and surface reactions for the ODHP process.

Water-Tolerant Boron-Substituted MCM-41 for Oxidative Dehydrogenation of Propane

Boron-based catalysts for oxidative dehydrogenation of propane (ODHP) have displayed excellent olefin selectivity. However, the drawback of deboronation leading to catalyst deactivation limited their scalable applications. Hereby, a series of mesoporous B-MCM-41 (BM-x, B/Si = 0.015-0.147) catalysts for ODHP were prepared by a simple hydrothermal synthesis method. It was found that propane conversion was increased and the initial reaction temperature was reduced with an increase of boron content, and the optimal values appeared on BM-2.0 (B/Si = 0.062), while olefins' (ethylene and propylene) selectivity was maintained at ca. 70-80%. Most importantly, BM-1.0 (B/Si = 0.048) exhibited favorable activity, stability, and water tolerance after washing treatment or long-time operation (e.g., propane conversion of ca. 15% and overall olefin selectivity of ca. 80% at 550 °C) because its high structural stability prevented boron leaches. These features were identified by X-ray diffraction (XRD), N₂ physisorption, inductively coupled plasma-mass spectrometry (ICP-MS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and solid-state magic-angle-spinning nuclear magnetic resonance (MAS NMR) spectroscopy studies. The tri-coordinated B-OH species incorporated into the mesoporous silica framework are considered to be the active sites for ODHP.

Efficient metal borate catalysts for oxidative dehydrogenation of propane

Boron-based catalysts have attracted attention due to their high selectivity to light olefins in the catalytic oxidative dehydrogenation of propane (ODHP) in the recent years, however, which still faced the...

Understanding the Unique Antioxidation Property of Boron-Based Catalysts during Oxidative Dehydrogenation of Alkanes

Boron-based catalysts show excellent performance in oxidative dehydrogenation (ODH) of light alkanes to alkenes with high selectivity and extremely good antioxidation properties. However, the anti-deep-oxidation mechanism remains unclear. Herein, we chose h-BN and B₂O₃ as representative boron-based catalysts to investigate their reactions with two important intermediates in the light alkane ODH, Et· (evolving to ethene) and EtO· (evolving to ethene or CO_x), to elucidate the origin of the antioxidation of alkanes. The density functional theory calculations reveal that surface boron sites could eliminate alkoxy in their vicinity, resulting in exceptional inhibition of alkane deep-oxidation. The analysis of the electronic and geometric structures of key stationary points showed that the oxophilicity of B determined the low deep-oxidation of alkanes, and the homoleptic coordination of B with all three ligating atoms being O moderately enhanced its oxophilicity. This work represents a novel conceptual advance in the mechanistic understanding of alkane ODH.

Oxidative dehydrogenation of light alkanes to olefins on metal-free catalysts

Metal-free boron- and carbon-based catalysts have shown both great fundamental and practical value in oxidative dehydrogenation (ODH) of light alkanes. In particular, boron-based catalysts show a superior selectivity toward olefins, excellent stability and atom-economy to valuable carbon-based products by minimizing CO2 emission, which are highly promising in future industrialization. The carbonaceous catalysts also exhibited impressive behavior in the ODH of light alkanes helped along by surface oxygen-containing functional groups. This review surveyed and compared the preparation methods of the boron- and carbon-based catalysts and their characterization, their performance in the ODH of light alkanes, and the mechanistic issues of the ODH including the identification of the possible active sites and the exploration of the underlying mechanisms. We discussed different boron-based materials and established versatile methodologies for the investigation of active sites and reaction mechanisms. We also elaborated on the similarities and differences in catalytic and kinetic behaviors, and reaction mechanisms between boron- and carbon-based metal-free materials. A perspective of the potential issues of metal-free ODH catalytic systems in terms of their rational design and their synergy with reactor engineering was sketched.

Current status and perspectives in oxidative, non-oxidative and CO2-mediated dehydrogenation of propane and isobutane over metal oxide catalysts

Conversion of propane or isobutane from natural/shale gas into propene or isobutene, which are indispensable for the synthesis of commodity chemicals, is an important environmentally friendly alternative to oil-based cracking processes.