Boron-Containing Catalysts for the Oxidative Dehydrogenation of Ethane/Propane Mixtures (original) (raw)
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Boron nitride for enhanced oxidative dehydrogenation of ethylbenzene
Journal of Energy Chemistry, 2020
It is demonstrated experimentally and confirmed theoretically that highly defective boron nitride showed outstanding performance for oxidative dehydrogenation of ethylbenzene. The catalyst is derived from carbon-doped hexagonal boron nitride nanosheets synthesized via a two-step reaction when participating the oxidative dehydrogenation reaction. The first step yields a polymeric precursor with the atomic positions of B, C, N relatively constrained, which is conducive for the formation of carbon atomic clusters uniformly dispersed throughout the BN framework. During the oxidative dehydrogenation of ethylbenzene to styrene, the nanoscale carbon clusters are removed and highly defective boron nitride (D-BN) is obtained, exposing boron-rich zigzag edges of BN that act as the catalytic sites. The catalytic performance of D-BN is therefore remarkably better than un-doped h-BN. Our results indicate that dispersed C-doping in h-BN is highly effective in terms of defect formation and resultant enhanced activity in oxidative dehydrogenation reactions.
Journal of Catalysis, 2002
Cobalt-and cobalt-boron-loaded TiO 2 (anatase) catalysts were prepared and characterized before and after catalytic tests by XRD, HRTEM, IR, UV-visible, and laser Raman spectroscopy. Their activity was investigated in oxidative dehydrogenation (ODH) of ethane. In the absence of boron, the best performances were exhibited by the sample containing 7.6 wt% Co, which was selected for further investigations. At 550 • C, it displayed a stationary state with a conversion of 22.2% and an ethylene selectivity around 60%. This catalyst also showed in the first 3 h on stream a 30% decay in activity that was attributed to a concomitant loss of specific surface area and the formation of CoTiO 3 and Co 2 TiO 4 phases. The addition of 0.25 wt% boron to this Co(7.6)/TiO 2 sample improved the ethane conversion and the ethylene selectivity, which attained 28.4 and 67%, respectively. Boron concentrations superior to 0.25 wt% negatively affected the catalysts performances, probably because at high loadings it profoundly modified the acid-base properties of the surface. XRD and HRTEM analyses showed that at the same time the size of Co 3 O 4 crystallites decreased. IR investigations confirmed the increase in acidity upon boron addition and the decrease in strength of the basic sites which were involved in the dehydrogenation processes. The catalytic behavior and the acid-base properties of Co(7.6)/TiO 2 loaded with different amounts of boron were also studied using butan-2-ol conversion. Boron addition enhanced the dehydration and the dehydrogenation reactions. However, above 0.25 wt% it decreased the dehydrogenation activity, confirming the modifications of the properties of the acid-base centers revealed by the IR studies. For this optimal concentration of boron, the activity and the selectivity in butan-2-ol dehydrogenation exhibited a maximum that coincided with the one observed in the ethane ODH, which suggests that both reactions possibly involved the same type of active centers.
Chinese Journal of Catalysis, 2019
Different mole ratio Al-B catalysts (Al-10B to Al-35B) were synthesized by using sol-gel (SG) method. Ethyl benzene (EB) dehydrogenation in the presence of oxygen and water steam was carried out on these catalysts at 450-500 °C with EB contact time of 0.54 gcat.s.cm-3. Acidity of Al-B catalysts was estimated by using NH3-TPD-mass spectral analysis studies. SEM-mapping images revealed fine distribution of boron up to 15% of its loading in alumina (Al-15B), whereas, boron aggregation was observed in higher boron content (Al-25B and Al-35B) catalysts. Essentially, acid sites of very weak strength (Tmax ≤ 125 °C) were observed for Al and Al-10B catalysts and resulted in low EB conversion and styrene yield. On the other hand, acid sites of weak strength (Tmax ≤ 180 °C) were observed for Al-25B and Al-35B catalysts and resulted in high EB conversion. However, greater styrene yield (43.2%) with reasonable EB conversion (46%) was obtained on acid sites of weak moderate strength in Al-15B catalyst. Further, Al-15B catalyst was synthesized by using co-precipitation (COP) and impregnation (IMP) methods. Acid sites related to NOx formation during the NH3-TPD-mass analysis on IMP and COP catalyst essentially improved the EB conversion to 66% and 63% respectively at 500 °C. However, these acid sites were diminished in Al-B SG catalyst and resulted in 50% of EB conversion at 500 °C. At 50% of EB conversion level, styrene selectivity of 73%, 82.5% and 84% were observed on Al-B IMP, Al-B COP and Al-SG catalysts, respectively. Hence, different method of preparation of Al-B catalyst generated acid sites of different strength and density and thereby influenced the styrene formation.
Oxidative dehydrogenation of propane over supported chromium–molybdenum oxides catalysts
Catalysis Communications, 2003
Oxidative dehydrogenation of propane using Ni-Mo-based metal oxide catalysts (without or with dopants: zinc and boron) was investigated in this paper. The catalysts were prepared, tested, and characterized by BET, SEM, XRD, and FTIR techniques. Higher propylene yields were obtained with alumina-supported catalysts compared to silica-supported ones, which showed much higher selectivity when doped with boron at lower propane conversions. Propylene yield was found to increase with increasing reaction temperatures and/or decreasing propane-to-oxygen ratios due to the increase in propane conversion.
Partial Oxidation of Methane to Methanol on Boron Nitride at Near Critical Acetonitrile
2021
Direct catalytic conversion of methane to methanol with O 2 has been a fundamental challenge in unlocking abundant natural gas supplies. Metal-free methane conversion with 17% methanol yield based on the limiting reagent O 2 at 275 °C was achieved with near supercritical acetonitrile in the presence of boron nitride. Reaction temperature, catalyst loading, dwell time, methane-oxygen molar ratio, and solvent-oxygen molar ratios were identified as critical factors controlling methane activation and the methanol yield. Extension of the study to ethane (C2) showed moderate yields of methanol (3.6%) and ethanol (4.5%).
In this work, we were able to significantly increase the activity of boron nitride catalysts used for the oxidative dehydrogenation (ODH) of propane by designing and synthesising boron nitride (BN) supported on dendritic fibrous nanosilica (DFNS). DFNS/BN showed a markedly increased catalytic efficiency, accompanied by exceptional stability and selectivity. Textural characterisation together with solid-state NMR and X-ray photoelectron spectroscopic analyses indicate the presence of a combination of unique fibrous morphology of DFNS and various boron sites connected to silica to be the reason for this increase in the catalytic performance. Notably, DFNS/B2O3 also showed catalytic activity, although with more moderate selectivity compared to that of DFNS/BN. Solid-state NMR spectra indicates that the higher selectivity of DFNS/BN might stem from a larger amount of hydrogen-bonded hydroxyl groups attached to B atoms. This study indicates that both boron nitride and oxide are active catalysts and by using high surface area support (DFNS), conversion from propane to propene as well as productivity of olefins was significantly increased.
Topics in Catalysis, 2020
A comparative study of the catalytic properties for the oxidation of C2-C3 alkanes and olefins has been carried out over unpromoted and M-promoted NiO catalysts (Me= K, La, Ce, al, Zr, Sn, Nb). The catalysts have been characterized by several physicochemical techniques (UV Raman, Visible Raman, FTIR of adsorbed CO and XPS). The characteristics of promoter elements are of paramount importance, since they are able to modify both the nature of the active nickel and the concentration of electrophilic O2-/Ooxygen species. Thus, a relatively high acidity and valence of the promoter oxide (with oxidation state higher than +3) are necessary to achieve high selectivity to olefins during the oxidative dehydrogenation (ODH) of C2-C3 alkanes. In addition, an inverse correlation between the selectivity to the corresponding olefin and the concentration of electrophilic oxygen species has been observed, although the selectivity to propene during propane ODH is lower than the selectivity to ethylene achieved during ethane ODH. On the other hand, a very low influence of alkane conversion on the selectivity to the corresponding olefins is observed. This behaviour can be explained by considering that the reaction rate for olefin combustion are lower to the reaction rate for alkane oxidation. However, the comparative study of the oxidation of alkanes and olefins suggest that the differences observed between the ODH of propane and ethane are not related to the reactivity of olefins, but to the different number and reactivity of C-H bonds in both alkanes. A discussion on the importance of the concentration of active sites and the characteristics of the alkanes fed on the selectivity to olefin during the alkane ODH is also presented.
Effect of boron on the stability of Ni catalysts during steam methane reforming
Journal of Catalysis, 2009
Ni catalysts promoted with 0.5 and 1.0 wt% boron were synthesized, characterized and tested during steam methane reforming, to evaluate the effect of boron on the deactivation behavior. Boron adsorbs on the γ-Al 2 O 3 support and on the Ni particles and 1.0 wt% boron is found to enhance the stability without compromising the activity. Catalytic studies at 800 • C, 1 atm, a stoichiometric methane to steam ratio, and space velocities of 330,000 cm 3 /(h g cat) show that promotion with 1.0 wt% boron reduces the rate of deactivation by a factor of 3 and increases the initial methane conversion from 56% for the unpromoted catalyst to 61%. Temperature-programmed oxidation (TPO) and scanning electron microscopy (SEM) studies confirm the formation of carbonaceous deposits and illustrate that 1.0 wt% boron reduces the amount of deposited carbon by 80%.
Catalytic Dehydrogenation of Ammonia Borane at Ni Monocarbene and Dicarbene Catalysts
Inorganic Chemistry, 2009
The development of ammonia borane (AB) as a promising hydrogen storage medium depends upon the ability to reversibly release H 2 from the system. We use density functional theory to investigate the mechanism of the catalytic dehydrogenation of AB by Ni N-heterocyclic carbene (NHC) complexes, which we show proceeds through Ni monocarbene and dicarbene species. Although Ni(NHC) 2 dehydrogenates AB, it competitively decomposes into a monocarbene species because AB readily displaces NHC from Ni(NHC) 2 and reaction of displaced NHC with abundant AB makes Ni monocarbene formation thermodynamically favored over the dicarbene catalyst. Prediction of NHC displacement by AB is consistent with the experimental observation of NHC-BH 3 . The Ni monocarbene species Ni(NHC)(NH 2 BH 2 ) competitively dehydrogenates AB with barriers consistent with the experimental temperature required to obtain reasonable reaction rates. The Ni monocarbene pathway also involves rate-limiting steps that exhibit both N-H and B-H kinetic isotope effects (KIEs), as observed experimentally. The predicted N-H and B-H KIEs are also in quantitative agreement with experiment. In contrast, AB dehydrogenation by Ni(NHC) 2 does not exhibit a B-H KIE. Activation of AB at both mono-and dicarbene catalysts proceeds through cis-carbene proton acceptance and involves transition states with significant electron delocalization over the π-system of the carbene and its phenyl rings. NHC Ni catalysts involving carbenes with substituent groups containing steric factors that preclude planarity of the phenyl rings to the carbene aromatic system, such as the Imes and Idipp ligands, are predicted to have lower reactivity, in agreement with experiment. The addition of electron donating and withdrawing groups to the phenyl rings demonstrate the importance of π-system electron delocalization by their influence on the barrier to cis-carbene proton acceptance.