Catalysts For Dehydrogenation Research Articles

Support Effect of Ga-Based Catalysts in the CO2-Assisted Oxidative Dehydrogenation of Propane

Carbon dioxide (CO2) assisted oxidative dehydrogenation of propane over Ga-modified catalysts is highly sensitive to the identity of support, but the underlying cause of support effects has not been well established. In this article, SSZ-13, SSZ-39, ZSM-5, silica and γ-Al2O3 were used to load Ga species by incipient wet impregnation. The structure, textural properties, acidity of the Ga-based catalysts and the process of CO2-assisted oxidative dehydrogenation of propane were examined by X-ray diffraction (XRD), nitrogen physisorption (N2 physisorption), ammonia temperature-programmed desorption (NH3-TPD), pyridine chemisorbed Fourier transform infrared spectra (Py-FTIR), OH-FTIR and in situ FTIR. Evaluation of the catalytic performance combined with detailed catalyst characterization suggests that their dehydrogenation activity is positively associated with the number of acid sites in middle strength, confirming that the Lewis acid sites generated by Ga cations are the active species in the reaction. Ga/Na-SSZ-39(9) also has feasible acidic strength and a unique channel structure, which is conducive to the dissociative adsorption of propane and desorption of olefins. The Ga/Na-SSZ-39(9) catalysts showed superior olefins selectivity and catalytic stability at 600 ℃ compared to any other catalysts. This approach to quantifying support acid strength, and channel structure and applying it as a key catalytic descriptor of support effects is a useful tool to enable the rational design of next-generation CO2-assisted oxidative dehydrogenation catalysts.

Research progress in design principles and mechanism regulation of dehydrogenation catalysts for liquid organic hydrogen carriers

Research progress in design principles and mechanism regulation of dehydrogenation catalysts for liquid organic hydrogen carriers

Nanoscale Ni-NiO-ZnO Heterojunctions for Switchable Dehydrogenation and Hydrogenation through Modulation of Active Sites.

Catalysts consisting of metal-metal hydroxide/oxide interfaces are highly in demand for advanced catalytic applications as their multicomponent active sites will enable different reactions to occur in close proximity through synergistic cooperation when a single component fails to promote it. To address this, herein we disclosed a simple, scalable, and affordable method for synthesizing catalysts consisting of nanoscale nickel-nickel oxide-zinc oxide (Ni-NiO-ZnO) heterojunctions by a combination of complexation and pyrolytic reduction. The modulation of active sites of catalysts was achieved by varying the reaction conditions of pyrolysis, controlling the growth, and inhibiting the interlayer interaction and Ostwald ripening through the efficient use of coordinated acetate and amide moieties of Zn-Ni materials (ZN-O), produced by the reaction between hydrazine hydrate and Zn-Ni-acetate complexes. We found that the coordinated organic moieties are crucial for forming heterojunctions and their superior catalytic activity. We analyzed two antagonistic reactions to evaluate the performance of the catalysts and found that while the heterostructure of Ni-NiO-ZnO and their cooperative synergy were crucial for managing the effectiveness and selectivity of the catalyst for dehydrogenation of aryl alkanes/alkenes, they failed to enhance the hydrogenation of nitro arenes. The hydrogenation reaction was influenced by the shape, surface properties, and interaction of the hydroxide and oxide of both zinc and nickel, particularly accessible Ni(0). The catalysts showed functional group tolerance, multiple reusabilities, broad substrate applicability, and good activity for both reactions.

Single‐Atom Fe Catalyst for Catalytic Ethane Dehydrogenation to Ethylene

AbstractThe single atom catalysts (SACs) show unique catalytic performance in heterogeneous reactions owing to unsaturated coordination sites and high metal atom dispersion. Herein, a simple wet impregnation method was utilized to synthetize of Fe−Al2O3 catalysts. The Fourier transformation infrared spectroscopy (FTIR) revealed that abundant OH group attached to the support (Al2O3) surface facilitating formation of isolated Fe single atom. High resolution transmission electron microscope (HR‐TEM) and extended X‐ray absorption fine structure (EXAFS) confirmed the Fe single atom architecture. Fe−Al2O3 (4.5 wt %) performed enhanced stability and activity on ethane dehydrogenation reaction.

EPR characterization of Cu/Al-Zr-Ce ethanol dehydrogenation catalysts: Active site development and coking control.

Electron paramagnetic resonance (EPR) spectroscopy was applied to study structure-performance relationships for copper-containing catalysts based on Al-Zr-Ce mixed oxides with various oxide support synthesis temperature. In situ EPR showed that the state of Cu2+ sites depends on the phase composition of the support, temperature, as well as the presence of the reaction medium during catalysis.

Facile construction of robust Ru-Co3O4 Mott-Schottky catalyst enabling efficient dehydrogenation of ammonia borane for hydrogen generation

Developing efficient catalysts for the dehydrogenation of ammonia borane (AB) is important for the safe storage and controlled release of hydrogen, but it is a challenging task. In this study, we designed a robust Ru-Co3O4 catalyst using the Mott-Schottky effect to induce favorable charge rearrangement. The self-created electron-rich Co3O4 and electron-deficient Ru sites at heterointerfaces are indispensable for the activation of the B-H bond in NH3BH3 and the OH bond in H2O, respectively. The synergistic electronic interaction between the electron-rich Co3O4 and electron-deficient Ru sites at the heterointerfaces resulted in an optimal Ru-Co3O4 heterostructure that exhibited outstanding catalytic activity for the hydrolysis of AB in the presence of NaOH. The heterostructure had an extremely high hydrogen generation rate (HGR) of 12238 mL min−1 gcat-1 and an expected high turnover frequency (TOF) of 755 molH2 molRu-1 min−1 at 298 K. The activation energy needed for the hydrolysis was low (36.65 kJ mol−1). This study opens up a new avenue for the rational design of high-performance catalysts for AB dehydrogenation based on the Mott-Schottky effect.

Structure-dependence and metal-dependence on atomically dispersed Ir catalysts for efficient n-butane dehydrogenation

Single-site pincer-ligated iridium complexes exhibit the ability for C-H activation in homogeneous catalysis. However, instability and difficulty in catalyst recycling are inherent disadvantages of the homogeneous catalyst, limiting its development. Here, we report an atomically dispersed Ir catalyst as the bridge between homogeneous and heterogeneous catalysis, which displays an outstanding catalytic performance for n-butane dehydrogenation, with a remarkable n-butane reaction rate (8.8 mol·gIr−1·h−1) and high butene selectivity (95.6%) at low temperature (450 °C). Significantly, we correlate the BDH activity with the Ir species from nanoscale to sub-nanoscale, to reveal the nature of structure-dependence of catalyst. Moreover, we compare Ir single atoms with Pt single atoms and Pd single atoms for in-depth understanding the nature of metal-dependence at the atomic level. From experimental and theoretical calculations results, the isolated Ir site is suitable for both reactant adsorption/activation and product desorption. Its remarkable dehydrogenation capacity and moderate adsorption behavior are the key to the outstanding catalytic activity and selectivity.

Regulating the C–H Bond Activation Pathway over ZrO2 via Doping Engineering for Propane Dehydrogenation

The efficient activation of the C–H bond in light alkanes and their catalyst design are significant for alkane-related catalytic processes in view of theoretical and practical aspects. Here, we report the C–H bond activation mechanism and structure–reactivity relationships of Ga-doped ZrO2 catalysts in propane dehydrogenation. Experimental and theoretical calculation results suggest that the introduction of Ga into the framework of ZrO2 alters the C–H bond activation pathway from a stepwise mechanism to a concerted mechanism involving simultaneous cleavage of two C–H bonds in propane, leading to a superior C–H bond activation ability and a lower reaction barrier than state-of-the-art metal oxide catalysts. In addition, a volcano-type dependence of the rate of propene formation on the Ga/Zr ratio is established due to a compromise of intrinsic activity and active site concentration. The strategy of metal incorporation into bulk metal oxide may provide an alternative solution to control the C–H bond activation pathway for efficient propene production.

Concerted oxygen diffusion across heterogeneous oxide interfaces for intensified propane dehydrogenation

Propane dehydrogenation (PDH) is an industrial technology for direct propylene production which has received extensive attention in recent years. Nevertheless, existing non-oxidative dehydrogenation technologies still suffer from the thermodynamic equilibrium limitations and severe coking. Here, we develop the intensified propane dehydrogenation to propylene by the chemical looping engineering on nanoscale core-shell redox catalysts. The core-shell redox catalyst combines dehydrogenation catalyst and solid oxygen carrier at one particle, preferably compose of two to three atomic layer-type vanadia coating ceria nanodomains. The highest 93.5% propylene selectivity is obtained, sustaining 43.6% propylene yield under 300 long-term dehydrogenation-oxidation cycles, which outperforms an analog of industrially relevant K-CrOx/Al2O3 catalysts and exhibits 45% energy savings in the scale-up of chemical looping scheme. Combining in situ spectroscopies, kinetics, and theoretical calculation, an intrinsically dynamic lattice oxygen “donator-acceptor” process is proposed that O2- generated from the ceria oxygen carrier is boosted to diffuse and transfer to vanadia dehydrogenation sites via a concerted hopping pathway at the interface, stabilizing surface vanadia with moderate oxygen coverage at pseudo steady state for selective dehydrogenation without significant overoxidation or cracking.

Sn1Pt single-atom alloy evolved stable PtSn/nano-Al2O3 catalyst for propane dehydrogenation

The PtSn/Al2O3 is a prototypical industrial catalyst for propane dehydrogenation (PDH). However, the local structures of the active sites are still inconclusive under the operation conditions. Herein, the evolutions of the Pt-Sn active centers supported on nano-Al2O3 are definitely discerned at the atomic level during PDH reaction. By combining complementary in situ characterizations and theoretical calculations, we demonstrate that a highly productive Sn1Pt single-atom alloy (47.6 molC3H6 gPt–1 h–1) forms after the reduction, and thereby self-assembles to the Pt3Sn intermetallic compound during the reaction, which exhibits a rather stable performance (kd-10~40h: 0.0026 h–1). Intriguingly, the results of in situ diffuse reflectance infrared Fourier-transform spectroscopy further corroborate that the adjacent Pt atoms with terrace sites aggravating the coke deposition can be circumvented through this single-atom alloy mediated reconstruction. Our findings depict an unprecedented evolution process of the active sites of the PtSn/Al2O3, and afford an effectual nanostructure engineering pathway for stable PDH catalysts.

Formation of active phases of Fe/C, Cr/C and Fe–Cr/C catalysts in oxidative dehydrogenation of ethane

The oxidative dehydrogenation of ethane into ethylene using CO2 as an oxidant at temperatures of 650–750 °C was carried out over Fe/C, Cr/C and Fe–Cr/C catalysts deposited on a carbon support. Before and after the reaction the catalysts were investigated by X-ray powder diffraction (XRD), in situ magnetometry and transmission electron microscopy methods. The correlation between activity of Fe/C, Cr/C and Fe–Cr/C catalytic systems and their phase composition was established.

Progressive formation of active and stable PtZn bimetallic nanoclusters by exsolution during propane dehydrogenation

PtZn bimetallic nanoclusters on two-dimensional (2D) molecular sieves are attractive catalysts for propane dehydrogenation (PDH) owing to the ease of molecular diffusion, resistance to deactivation by coke deposition, and electronic promotion by Zn. Here, we report the progressive formation of highly active PtZn bimetallic nanoclusters on a Pt-modified zincosilicate with 2D delaminated MWW layers (PtZn-DML) under PDH conditions. The exsolution of Zn from the zincosilicate DML framework during PDH generates highly dispersed PtZn active sites and reduces the Lewis acidity of zincosilicate DML support, resulting in a high propane conversion (40.3%) comparable to thermodynamic equilibrium as well as extraordinary stability with a low deactivation rate (kd < 0.002 h−1) up to 13.6 days.

Evaluation of bimetallic Pt–Co and Pt–Ni catalysts in LOHC dehydrogenation

Liquid Organic Hydrogen Carrier (LOHC) systems offer the possibility of long-period hydrogen storage without losses. PGM-based catalysts have been extensively studied for their use in the LOHC hydrogenation (hydrogen storage) and also in dehydrogenation (hydrogen production) reactions. However, during the dehydrogenation a high PGM/LOHC ratio is necessary to achieve significant conversions. In this work, the influence of non-noble metal (Co and Ni) incorporation over Pt-based catalyst with low metal content (0.5 wt% Pt) was studied. It has been demonstrated that Pt–Co and Pt–Ni interactions increase for lower non noble metal contents, which result in higher bimetallic performance in dehydrogenation. The addition of 0.5 wt% Co resulted to increase the dehydrogenation productivity, while the Ni incorporation did not improve the performance of the monometallic Pt catalysts.

Investigation on deactivation of Cu-Cr catalyst for direct ethanol dehydrogenation to ethyl acetate, acetaldehyde, and hydrogen

BackgroundThe utilization of bioethanol by converting it into additional high-value-added products including acetaldehyde, ethyl acetate, and hydrogen impresses as an appealing strategy at the present. The Cu-Cr catalysts improved product formation on ethanol dehydrogenation. This research was to assess the stability of the reaction and the deactivation of the catalyst over protracted ethanol dehydrogenation. MethodsThe deactivation behaviors of 50 Cu-Cr catalyst on ethanol dehydrogenation reaction was investigated. The co-precipitation technique was used to synthesize the Cu-Cr catalyst, which was then reduced by a mixture of H2/N2 prior to the stability test in the ethanol dehydrogenation reaction. The fresh, reduced, and/or spent catalysts after being used in ethanol dehydrogenation were characterized using XRD, SEM-EDX, HR-TEM, H2-TPR, NH3-TPD, XPS, TGA, and TPO. Significant findingThe proportion of CuCr2O4, Cu+, and Cu0 active sites on the catalyst sample influenced catalytic activity. Based on the results, the activity was related to the oxidation state of copper-chromium in the Cu-Cr catalyst. Fascinatingly, the results of the ethanol dehydrogenation showed that the catalyst deactivation was caused by the change in the copper-chromium oxidation state via the hydrogen self-reduction process and the soft coke formation on active sites after prolonged ethanol dehydrogenation resulting in a decrease in catalytic activity.

Fast and Durable Dehydrogenation of Formic Acid over Pd–Cr(OH)3 Nanoclusters Immobilized on Amino-Modified Reduced Graphene Oxide

Formic acid, attractive as a renewable and safe liquid organic hydrogen carrier (LOHC), can be obtained by biomass conversion and CO2 hydrogenation with green hydrogen. The efficient and durable catalysts for formic acid dehydrogenation (FAD) are beneficial in the industry. Herein, Cr(OH)3-promoted Pd nanoclusters (NCs) (i.e., 1.6 nm) immobilized on amino-modified reduced graphene oxide (NH2-rGO) were successfully prepared through a simple wet-chemical approach. The obtained Pd–Cr(OH)3/NH2-rGO catalyst exhibits excellent catalytic activity and 100% hydrogen selectivity for CO-free FAD, giving a high turnover frequency of 2519.5 h–1 at 323 K, outperforming most reported Pd-based heterogeneous catalysts. Especially, the catalyst possesses robust durability toward FAD with no significant decline in activity and aggregation of metal NCs even after 10 cycles. The superior performance of the catalyst may be ascribed to the well-distributed Pd–Cr(OH)3 NCs, the strong electronic coupling of Pd with Cr(OH)3, the synergetic interaction of Pd–Cr(OH)3 with NH2-rGO, and the promotion effect of amino group. The reaction mechanism of FAD was explored based on the isotope experiments. This work provides insights into designing an effective and durable heterogeneous catalyst for dehydrogenation of LOHC.

Sub-nanometer Pt2In3 intermetallics as ultra-stable catalyst for propane dehydrogenation

Pt-based catalysts are the typical industrial catalysts for propane dehydrogenation (PDH), which still suffer from insufficient long-term durability due to the structural instability and coke deposition. A commercial γ-Al2O3 supported thermally robust sub-nanometer Pt2In3 intermetallic catalyst with atomically ordered structure and rigorously separated Pt single atoms was fabricated, which showed outstanding robustness in 240 h long-term operation at 600 °C with the deactivation rate constant kd as low as 0.00078 h−1, ranking among the lowest reported values. Based on various in situ characterizations and theoretical calculations, it was proved that the catalyst stability not only resulted from the separated Pt single-atom sites but also significantly affected by the distance of adjacent Pt atoms. An increasing distance to 3.25 Å in the Pt2In3 could induce a weak π-adsorption configuration of propylene on Pt sites, which facilitated the desorption of propylene and restrained the side reactions like coking.

Nanostructured bimetallic Zn/Co in N-doped carbon as an efficient catalyst for the alcohol dehydrogenation to carboxylic acids under solvent-free conditions

The catalytic alcohol dehydrogenation to carboxylic acids has been demonstrated as an atom-economic and environmental-friendly synthetic method. However, the reported catalysts either require relatively complicated synthesis or exhibit high activity only in the presence of a solvent. Therefore, it is still in high demand to obtain catalysts that feature facile synthesis and perform well even without any solvent. Herein, a series of nanostructured bimetallic Zn/Co species embedded in N-doped hierarchical porous carbon were fabricated in a facile and green manner. More significantly, the best-performing material (Zn/Co@NC-800) was identified as the first heterogeneous catalyst to enable this transformation under solvent-free conditions. Moreover, the as-prepared composites were comprehensively investigated to determine their structural and morphological properties, which rationalized the superiority of Zn/Co@NC-800 over the other synthesized materials. Further studies signified that Co sites (both Co0 and Co2+) and N species (mainly pyridinic N) were probably involved in this process, functioning as the Lewis acid site and basic site, respectively. Hopefully, this study could provide a simple and sustainable method for carboxylic acid synthesis.

A highly active Pd clusters hosted by magnesium hydroxide nanosheets promoting hydrogen storage

Liquid organic hydrogen carriers (LOHCs) represent promising candidates for large-scale hydrogen storage, yet the design of high-efficiency and low-cost catalysts on the dehydrogenation of LOHCs remains challenging. Herein, we develop a two-dimensional (2D) magnesium hydroxide nanosheet that hosts Pd clusters (Pd/Mg(OH)2) for the dehydrogenation of dodecahydro-N-ethylcarbazole (12H-NEC), an important reaction for H2 transportation. The catalyst boosts the activity up to a 12H-NEC conversion of 100 % and the hydrogen release of 5.72 wt% with a low metal loading of 0.5 wt%, while the hydrogen release on Pd/MgO is only 2.34 wt% with the conversion rate of 71 % under the same conditions. Coupling various characterization technologies (HAADF-STEM, EXAFS, EPR and In-situ DRIFTS) with DFT calculations, it was found that the work function of magnesium hydroxide nanosheets for the dehydrogenation reaction due to the strong metal-support interaction, which makes Pd species have better dispersion, forms Pdn+-OH stable Pd cluster and reduces the dehydrogenation barrier as well, thus enhancing the dehydrogenation performance and improving the hydrogen production greatly. This work provides a new promising way to design advanced dehydrogenation catalyst with high activity for the hydrogen storage.

Elucidation of puzzling questions regarding the CrOx/Al2O3 catalyst I. X-ray absorption spectroscopy aided identification of the nature of the chromium oxide species in the CrOx/Al2O3 dehydrogenation catalyst system

The CATOFIN© process produces propylene from propane using a CrOx /Al2O3 catalyst. Despite its use, there are still uncertainties surrounding the nature of Cr species formed during synthesis, regeneration, and aging. It has been observed that ppm levels of Cr2O3 can be oxidized to Cr(VI) in air; however, when Cr2O3 is in direct contact with Al2O3, Cr(VI) formation increased more than 100-fold. To confirm physical contact between Cr2O3 and Al2O3 results in increased Cr(VI) formation, Cr2O3 and Cr2O3/Al2O3 samples were synthesized, calcined, and characterized. Catalytic activity measurements confirm propylene selectivity inversely tracks with Cr(VI). Wet chemical titration and X-ray absorption spectroscopy (XAS) quantified and determined the structure of the Cr(VI) species. FEFF X-ray absorption near edge structure simulations determined the potential sensitivity of the XAS to the presence of Al3+/Cr3+ neighboring atoms. XAS correlated to FEFF simulations suggested that Al3+xCr3+2−xCr6+3O12 comprises a significant fraction of the Cr(VI) species formed.

Enhancement of ethylene production by alkali metal doping of MoVSb mixed oxide catalyst for ethane oxidative dehydrogenation

Hydrothermally prepared Mo-V-Sb mixed oxides doped with alkali metal cations (Li+, Na+, K+, Rb+, or Cs+) show a significantly improved catalytic behavior in the oxidative dehydrogenation of ethane (ODH) compared to conventional alkali metal-free MoVSbO catalysts. Initial selectivity to ethylene above 95 % was held up to 20 % of ethane conversion for all alkali metal promoted MoVSbO catalysts, as well as lower ethylene overoxidation at higher ethane conversion, with differences depending on the alkali metal employed. Thus, from Li to K, the enhanced catalytic performance follows a bottom-up trend as increasing the size of the cation. An intermediate behavior is observed though for the catalyst doped with Cs cations, with the highest atomic radius. The K-doped MoVSbO catalyst is the least prone to both ethane total oxidation and ethylene overoxidation, which enables up to 90 % selectivity to ethylene at ethane conversion higher than 65 %.