Selective Dehydrogenation Research Articles

Formic Acid Dehydrogenation by a Cyclometalatedκ3‐CNN Ruthenium Complex

Hydrogen utilization as a sustainable energy vector is of growing interest. We report herein a cyclometalated ruthenium complex [Ru(κ3‐CNN)(dppb)Cl], originally described by Baratta, to be active in the selective dehydrogenation (DH) of formic acid (FA) to H2and CO2. TON's of more than 10000 were achieved under best conditions without observation of CO (detection limit 10 ppm). The distinguished behavior of the catalyst was explored varying the starting conditions. Our observation revealed the complex [Ru(κ3‐CNN)(dppb)(OOCH)] as key species in the catalytic cycle.

Spherical Superstructure of Boron Nitride Nanosheets Derived from Boron-Containing Metal-Organic Frameworks.

The assembly of two-dimensional (2D) nanosheets into three-dimensional (3D) well-organized superstructures is one of the key topics in materials chemistry and physics, due to their potential applications in various fields. Herein, starting from the crystalline metal-organic framework (MOF) particles, a spherical superstructure consisting of metal-organic framework nanosheets (SS-MOFNSs) is synthesized via a simple solvothermal transformation process. After pyrolysis and nitrogenization in ammonia, the SS-MOFNSs are further transformed into the spherical superstructure consisting of boron nitride nanosheets (SS-BNNSs), which preserve the original spherical superstructure morphology. Taking advantage of this unique superstructure, the resulting SS-BNNSs exhibit excellent catalytic activity for selective oxidative dehydrogenation of propane to produce propylene and ethylene. The results of this work provide a novel synthetic strategy to fabricate 3D spherical superstructures consisting of 2D nanosheets for high-performance applications in catalysis, energy storage, as well as other related fields.

Selective Acceptorless Dehydrogenation of Primary Amines to Imines by Core-Shell Cobalt Nanoparticles.

Core–shell nanocatalysts are attractive due to their versatility and stability. Here, we describe cobalt nanoparticles encapsulated within graphitic shells prepared via the pyrolysis of a cationic poly‐ionic liquid (PIL) with a cobalt(II) chloride anion. The resulting material has a core–shell structure that displays excellent activity and selectivity in the self‐dehydrogenation and hetero‐dehydrogenation of primary amines to their corresponding imines. Furthermore, the catalyst exhibits excellent activity in the synthesis of secondary imines from substrates with various reducible functional groups (C=C, C≡C and C≡N) and amino acid derivatives.

Selective Acceptorless Dehydrogenation of Primary Amines to Imines by Core–Shell Cobalt Nanoparticles

AbstractCore–shell nanocatalysts are attractive due to their versatility and stability. Here, we describe cobalt nanoparticles encapsulated within graphitic shells prepared via the pyrolysis of a cationic poly‐ionic liquid (PIL) with a cobalt(II) chloride anion. The resulting material has a core–shell structure that displays excellent activity and selectivity in the self‐dehydrogenation and hetero‐dehydrogenation of primary amines to their corresponding imines. Furthermore, the catalyst exhibits excellent activity in the synthesis of secondary imines from substrates with various reducible functional groups (C=C, C≡C and C≡N) and amino acid derivatives.

Microwave-activated structured reactors to maximize propylene selectivity in the oxidative dehydrogenation of propane

Abstract Microwave (MW) heating has been applied to increase the selectivity to propylene in the oxidative dehydrogenation (ODH) of propane. The preferential heating of the solid monolith (made of SiC, a good microwave susceptor), allows working with a lower gas phase temperature, reducing the formation of undesired by-products in the gas phase via homogeneous reactions. Conversion levels of ~ 21% and selectivity to propylene up to 70% have been achieved with MW-heated straight channel monolithic reactors coated with a VMgO catalyst. These competitive values contrast with the more limited performance delivered by the same catalytic system when it is subjected to conventional heating in a fixed-bed reactor configuration, thereby corroborating the advantage of working under a significant gas–solid temperature gap to minimize the extent of homogeneous reactions.

Crafting Porous Carbon for Immobilizing Pd Nanoparticles with Enhanced Catalytic Activity for Formic Acid Dehydrogenation

AbstractThe development of highly active heterogeneous catalytic systems that catalyze formic acid (FA) to generate CO‐free H2 holds great promise for future energy demands, but is often limited by the low catalytic activity and stability of metal catalysts under ambient conditions. It is thus highly desirable to rationally design a catalyst to boost the catalytic performance. Herein, a general room‐temperature HNO3‐treatment approach (RTHTA) is developed to accomplish surface modification of various porous carbon materials for immobilizing ultrafine palladium nanoparticles (Pd NPs). A significantly enhanced catalytic performance of the immobilized Pd NPs toward the selective dehydrogenation of FA is achieved, which gives a record‐high turnover frequency of 13333 h−1 at 60 °C, corresponding to a calculated H2 generation rate of 50.8 L H2 min−1 gPd−1. The results presented here may provide insight into the formation and stabilization of highly active immobilized metal nanoparticles, as well as the enhanced catalytic performance of Pd NPs for catalytic dehydrogenation reactions.

Synergy between oxides of Ni and Ca for selective catalytic lactic acid synthesis from glycerol in a single step process

Single-step selective catalytic dehydrogenation of glycerol to lactic acid requires a catalyst with strong dehydrogenation and hydration capabilities. A multi-component catalyst consisting of an alkaline earth metal and assisted by a transition metal is deemed essential to achieve yield lactic acid in this multi-step reaction. A series of NiO/CaO catalysts with different Ni/Ca ratios were synthesized via a co-precipitation method and tested for their catalytic activity. The physicochemical properties of the catalysts were studied through TGA, SEM, N2-adsorption, CO2-TPD and XRD analyses. The NiO particles were relatively smaller than those of CaO to enable their deposition on the surface of the latter. High amounts of basic sites of more than 4.84mmol/gcat were detected on the NiO/CaO catalysts. The lactic acid yield was strongly influenced by the molar ratio of the NiO/CaO catalysts due to their improved dehydrogenation and hydration capabilities. The synergy between NiO with CaO in the catalyst was also elucidated. The 0.43NiO/CaO catalyst exhibited desirable activity with 41.4% lactic acid yield at 89.3% glycerol conversion. A catalyst loading of 15wt. %, a reaction temperature of 290°C and 1.5h of reaction time were needed to achieve this conversion. Thus, the combination of NiO/CaO resulted in the synergy towards achieving better lactic acid yield in this selective conversion to lactic acid. However, accurate control of the reaction was critical as the intermediates and lactic acid were highly reactive to participate in other side-reactions.

Isolated Indium Hydrides in CHA Zeolites: Speciation and Catalysis for Nonoxidative Dehydrogenation of Ethane.

The study of the formation, characterization, and functionality of isolated surface hydrides on solid materials is a formidable task because of the complexity of solid surfaces and the difficulty of analyzing structures in solids. Herein, we found the formation of indium (In) hydride species supported by CHA zeolites. The In hydrides were formed by treatment of an In-exchanged CHA zeolite (In-CHA) with H2 at high temperatures (>773 K). In situ Fourier transform infrared (FTIR) spectroscopy and density functional theory (DFT) calculations revealed that an [InH2]+ ion on a framework anionic site is a plausible structure. In-CHA exhibited high selectivity and durable catalytic activity for the nonoxidative dehydrogenation of ethane for at least 90 h. Kinetic and in situ spectroscopic studies as well as transition state (TS) calculations suggested that [InH2]+ ions serve as catalytically active sites for selective dehydrogenation using In-CHA.

Research on the Selectivity and Activity of Ethane Oxidation Dehydrogenation with CO 2 on Cr‐based Catalyst

Catalysts containing different Cr load (5 %∼15 %) supported on SiO2 were prepared using the incipient wetness impregnation method. The influence of Cr load was investigated for the ethane oxidation dehydrogenation with CO2 and the difference between Co, Fe and Cr were compared. The catalytic activity is affected by the load of the Cr/SiO2.Cr-10 %/SiO2 exhibits best catalytic performance, providing ethane conversion of 30.53 % as well as 98.64 % ethylene selectivity at 650 °C. Excessive load increases the aggregation and grain size of active phase, which goes against catalytic activity. Furthermore, overload increases the crystallization of α-Cr2O3, which is difficult for reduction and is adverse for catalytic activity. Ethane conversion of Cr, Co and Fe based catalysts is corresponding to redox ability. Cr-10 %/SiO2(30.53 %) takes the lead and Fe-10 %/SiO2 is the least active (18.98 %). Co-10 %/SiO2 is suitable for reforming reaction as its ethylene selectivity is only 19.60 % at 650 °C.

Microwave synthesis of nanocrystalline LaCoO3 samples and their catalytic activity towards decomposition of isopropanol

Nanocrystalline LaCoO3 powders were fabricated via the sol–gel microwave-induced combustion approach using metal nitrates as oxidant and citric acid as fuel. Calcination of the precursor was performed in the temperature range 400–800 °C. The precursor of the LaCoO3 powder as well as the calcination products were investigated using thermal analysis (TGA and DTA), FTIR, XRD and N2 adsorption techniques. In a dynamic air atmosphere, calcination was implemented in the temperature range 400–800 °C. XRD patterns show the fabrication of the perovskite rhombohedral phase of LaCoO3. The average nanoparticle size calculated from the XRD patterns was in the range 8–21 nm. Surface area measurements calculated from the N2 adsorption isotherms show low surface area values. The porosity of these materials was identified to be microporous in nature. SEM and TEM tests endorsed the findings. Analysis of TGA and DTA showed a sharp exothermic peak of about 358 °C and a steady weight loss of up to about 600 °C. The vapor-phase dehydration/dehydrogenation of isopropanol, in the temperature range 350–425 °C, was adopted to assess the catalytic performance. The activity of the LaMnO3 catalysts is mainly directed towards the dehydrogenation reaction forming acetone as a main product. The maximum yield was found for the sample calcined at 600 °C. A strong correlation was identified between the selectivity of dehydrogenation and the redox couple species evaluated. A potential reaction mechanism was suggested that would be compatible with the data obtained.

Single‐Site Catalysts: Hierarchical Porous Organometallic Polymers Fabricated by Direct Knitting: Recyclable Single‐Site Catalysts with Enhanced Activity (Adv. Mater. 6/2020)

A crucial bottleneck hampering the application of immobilized catalysts is their reduced catalytic activity. In article number 1905950, Tao Tu and co-workers describe the preparation of porous organometallic polymers with atomically dispersed metal centers and hierarchical pores by direct knitting of privileged N-heterocyclic metal complexes. Dramatically enhanced catalytic activity (750 times higher) and selectivity in both dehydrogenation and hydrogenation reactions is demonstrated.

Enhancing selectivity and reducing cost for dehydrogenation of dodecahydro-N-ethylcarbazole by supporting platinum on titanium dioxide

N-ethylcarbazole/dodecahydro-N-ethylcarbazole (NECZ/12H-NECZ) was a promising system for hydrogen storage applications. 1.0 wt% Pt/TiO2 was regarded as the optimal loading in Pt/TiO2 catalyst applied in the 12H-NECZ dehydrogenation reaction. The hydrogen release amount, selectivity to NECZ and TOF of 12H-NECZ dehydrogenation are 5.75 wt %, 98% and 229.73 min−1 at 453 K. Compared with the commercial 5.0 wt% Pd and Pt-based catalysts, it exhibited very high activity, selectivity and stability for 12H-NECZ dehydrogenation with low Pt loading. Combined with the XRD, XPS, HRTEM, TPR analysis, it was indicated that the enhanced catalytic performance was due to the SMSI (strong metal-supporting interaction) between Pt and TiO2 support, which accelerated the rate-limiting step and enhanced the whole dehydrogenation reaction. This work may be beneficial for the commercial application of Pt/TiO2 catalysts in the Liquid Organic Hydrogen Carrier (LOHC) system.

Atomic Layer Deposition for Preparing Isolated Co Sites on SiO2 for Ethane Dehydrogenation Catalysis.

Unlike Co clusters, isolated Co atoms have been shown to be selective for catalytic dehydrogenation of ethane to ethylene; however, preparation of isolated Co sites requires special preparation procedures. Here, we demonstrate that Atomic Layer Deposition (ALD) of tris(2,2,6,6-tetramethyl-3,5-heptanedionato)cobalt(III) (Co(TMHD)3) on silica and other supports is effective in producing these isolated species. Silica-supported catalysts prepared with one ALD cycle showed ethylene selectivities greater than 96% at 923 K and were stable when CO2 was co-fed with the ethane. Co catalysts prepared by impregnation formed clusters that were significantly less active, selective, and stable. Rates and selectivities also decreased for catalysts with multiple ALD cycles. Isolated Co catalysts prepared on Al2O3 and MgAl2O4 showed reasonable selectivity for ethane dehydrogenation but were not as effective as their silica counterpart.

Selective Dehydrogenative Acylation of Enamides with Aldehydes Leading to Valuable β-Ketoenamides.

We have presented a unique example of dehydrogenative acylation of enamides with aldehydes enabled by an earth-abundant iron catalyst. The protocol provides the straightforward access to valuable β-ketoenamides with ample substrate scope and excellent functional group tolerance. Notably, distinct C-H acylation of enamide rather than at N-H moiety site occurs with absolute Z-selectivity was observed. Late-stage modifications of complex molecules and versatile synthetic utility of β-ketoenamides further highlight the practicability of this transformation.

Atomically Dispersed Pd Supported on Zinc Oxide for Selective Nonoxidative Ethanol Dehydrogenation

Atomically dispersed Pd/ZnO was synthesized using a facile method. We found that 0.07 wt % Pd was isolated and positively charged on ZnO synthesized using a solvothermal method. By contrast, Pd clu...

Selective formic acid dehydrogenation at low temperature over a RuO2/COF pre-catalyst synthesized on the gram scale

Selective formic acid dehydrogenation over an efficient RuO2/COF pre-catalyst with good dispersion of the active metal and large N-content on the COF support.

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

Boron containing catalysts have great potential in the oxidative dehydrogenation of propane. Herein, a series of 15, 25 and 42 at% boron-hyperdoped silicon catalysts synthesized by laser pyrolysis was studied. Boron-hyperdoped silicon samples showed >6 times higher propylene productivity than commercial h-BN at 450 °C.

Oxidative dehydrogenation of propane over transition metal sulfides using sulfur as an alternative oxidant

Sulfur vapor (S2) is explored as a “soft” oxidant for the selective catalytic dehydrogenation of propane to propylene over a variety of metal sulfide surfaces.

DFT studies on the reaction mechanism for the selective oxidative dehydrogenation of light alkanes by BN catalysts

The oxidative dehydrogenation (ODH) reaction mechanism of ethane and propane catalyzed by two kinds of oxygen-species-terminated BN materials, namely BN nanotubes and h-BN, was studied by the B3LYP-D3 functional with the 6-31G(d,p) basis set.

Structural trends in the dehydrogenation selectivity of palladium alloys.

Alloying is well-known to improve the dehydrogenation selectivity of pure metals, but there remains considerable debate about the structural and electronic features of alloy surfaces that give rise to this behavior. To provide molecular-level insights into these effects, a series of Pd intermetallic alloy catalysts with Zn, Ga, In, Fe and Mn promoter elements was synthesized, and the structures were determined using in situ X-ray absorption spectroscopy (XAS) and synchrotron X-ray diffraction (XRD). The alloys all showed propane dehydrogenation turnover rates 5–8 times higher than monometallic Pd and selectivity to propylene of over 90%. Moreover, among the synthesized alloys, Pd3M alloy structures were less olefin selective than PdM alloys which were, in turn, almost 100% selective to propylene. This selectivity improvement was interpreted by changes in the DFT-calculated binding energies and activation energies for C–C and C–H bond activation, which are ultimately influenced by perturbation of the most stable adsorption site and changes to the d-band density of states. Furthermore, transition state analysis showed that the C–C bond breaking reactions require 4-fold ensemble sites, which are suggested to be required for non-selective, alkane hydrogenolysis reactions. These sites, which are not present on alloys with PdM structures, could be formed in the Pd3M alloy through substitution of one M atom with Pd, and this effect is suggested to be partially responsible for their slightly lower selectivity.