Effect of group IB metals on the dehydrogenation of propane to propylene over anti-sintering Pt/MgAl2O4

Boosting Propane Dehydrogenation to Propylene via Electron Hole-Hydrogen Coupling on Cobalt Metal Surface

Nonoxidative dehydrogenation of propane is useful for the high selectivity to propylene but is suffering from the heavy coke deposition on the catalyst surface. Herein, we present a proof-of-concept application of a hole-hydrogen (H) couple on a metallic cobalt surface to decrease the deactivation rate. The coupled H atoms on the Cobalt (Co) surface, partially resulting from propane dehydrogenation, enabled the desorption of propylene to avoid deep hydrogenolysis and coke deposition and realize selective and durable propylene production, while conventional Co metal-based catalysts do not generate propylene. The optimized hole-H coupled Co catalyst provided a low deactivation rate (0.0036 h-1) and a high turnover frequency (55.6 h-1) for propylene production with a high propane flux (48 vol.% C3H8 in gas feeds) at 550 °C.

Engineering Oxygen Vacancies of Co-Mn-Ni-Fe-Al High-Entropy Spinel Oxides by Adjusting Co Content for Enhanced Catalytic Combustion of Propane

Transition metal-based oxides with similar oxidation activities for catalytic hydrocarbon combustion have attracted much attention. In this study, a new class of metal high-entropy oxides (CoxMnNiFeAl)3O4 (x = 1, 2, 3, 4, 5) with a porous structure was fabricated through a simple and inexpensive NaCl template-assisted sol-gel approach, which was employed for the catalytic oxidation of propane. The results indicated that the content of cobalt has a great impact on its activity, and the (Co4MnNiFeAl)3O4 catalyst exhibited the best catalytic activity. At the high space velocity of 60 000 mL·g-1·h-1, the optimized one with high-temperature treatment can still achieve 90% propane conversion at 309 °C, which is 68 and 178 °C lower than those of the (CoMnNiFeAl)3O4 catalyst and pure cobalt oxide, respectively. Meanwhile, it has the lowest apparent activation energy (46.6 KJ·mol-1) and the fastest reaction rate (26.976 × 10-6 mol·gcat-1·s-1 at 290 °C). The improved performance of the (Co4MnNiFeAl)3O4 catalyst could be attributed to the enhancement of low-temperature reducibility, the increased number of reactive surface oxygen species, and the cocktail effect of the high-entropy oxides. This work provides new insights into the preparation of efficient light alkane degradation catalysts and a realistic approach for the large-scale application of high-entropy oxides in the field of oxidation catalysts.

Carbon-Boosted and Nitrogen-Stabilized Isolated Single-Atom Sites for Direct Dehydrogenation of Lower Alkanes

Lower olefins are widely used in the chemical industry as basic carbon-based feedstocks. Here, we report the catalytic system featuring isolated single-atom sites of iridium (Ir1) that can function within the entire temperature range of 300-600 °C and transform alkanes with conversions close to thermodynamics-dictated levels. The high turnover frequency values of the Ir1 system are comparable to those of homogeneous catalytic reactions. Experimental data and theoretical calculations both indicate that Ir1 is the primary catalytic site, while the coordinating C and N atoms help to enhance the activity and stability, respectively; all three kinds of elements cooperatively contribute to the high performance of this novel active site. We have further immobilized this catalyst on particulate Al2O3, and we found that the resulting composite system under mimicked industrial conditions could still give high catalytic performances; in addition, we have also developed and established a new scheme of periodical in situ regeneration specifically for this composite particulate catalyst.

Formation of a Porous Crystalline Mg1-xAl2Oy Overlayer on Metal Catalysts via Controlled Solid-State Reactions for High-temperature Stable Catalysis

Catalyst deactivation by sintering and coking is a long-standing issue in metal-catalyzed harsh high-temperature hydrocarbon reactions. Ultrathin oxide coatings of metal nanocatalysts have recently appeared attractive to address this issue, while the porosity of the overlayer is difficult to control to preserve the accessibility of embedded metal nanoparticles, thus often leading to a large decrease in activity. Here, we report that a nanometer-thick alumina coating of MgAl2O4-supported metal catalysts followed by high-temperature reduction can transform a nonporous amorphous alumina overlayer into a porous Mg1-xAl2Oy crystalline spinel structure with a pore size of 2-3 nm and weakened acidity. The high porosity stems from the restrained Mg migration from the MgAl2O4 support to the alumina overlayer through solid-state reactions at high temperatures. The resulting Ni/MgAl2O4 and Pt/MgAl2O4 catalysts with a porous crystalline Mg1-xAl2Oy overlayer achieved remarkably high stability while preserving much higher activity than the corresponding alumina-coated Ni and Pt catalysts on MgO and Al2O3 supports in the reactions of dry reforming of methane and propane dehydrogenation, respectively.

Microwave-assisted, performance-advantaged electrification of propane dehydrogenation

Nonoxidative propane dehydrogenation (PDH) produces on-site propylene for value-added chemicals. While commercial, its modest selectivity and catalyst deactivation hamper the process efficiency and limit operation to lower temperatures. We demonstrate PDH in a microwave (MW)-heated reactor over PtSn/SiO2 catalyst pellets loaded in a SiC monolith acting as MW susceptor and a heat distributor while ensuring comparable conditions with conventional reactors. Time-on-stream experiments show active and stable operation at 500°C without hydrogen addition. Upon increasing temperature or feed partial pressure at high space velocity, catalysts under MWs show resistance in coking and sintering, high activity, and selectivity, starkly contrasting conventional reactors whose catalyst undergoes deactivation. Mechanistic differences in coke formation are exposed. Gas-solid temperature gradients are computationally investigated, and nanoscale temperature inhomogeneities are proposed to rationalize the different performances of the heating modes. The approach highlights the great potential of electrification of endothermic catalytic reactions.

Support stabilized PtCu single-atom alloys for propane dehydrogenation

PtCu single-atom alloys (SAAs) open an extensive prospect for heterogeneous catalysis. However, as the host of SAAs, Cu suffers from severe sintering at elevated temperature, resulting in poor stability of catalysts. This paper describes the suppression of the agglomeration of Cu nanoparticles under high temperature conditions using copper phyllosilicate (CuSiO3) as the support of PtCu SAAs. Based on quasi in situ XPS, in situ CO-DRIFTS, in situ Raman spectroscopy and in situ XRD, we demonstrated that the interfacial Cu+-O-Si formed upon reduction at 680 °C serves as the adhesive between Cu nanoparticles and the silicon dioxide matrix, strengthening the metal-support interaction. Consequently, the resistance to sintering of PtCu SAAs was improved, leading to high catalytic stability during propane dehydrogenation without sacrificing conversion and selectivity. The optimized PtCu SAA catalyst achieved more than 42% propane conversion and 93% propylene selectivity at 580 °C for at least 30 hours. It paves a way for the design and development of highly active supported single-atom alloy catalysts with excellent thermal stability.

Advanced design and development of catalysts in propane dehydrogenation

Propane dehydrogenation (PDH) is an industrial technology for direct propylene production, which has received extensive attention and realized large-scale application. At present, the commercial Pt/Cr-based catalysts suffer from fast deactivation and inferior stability resulting from active species sintering and coke depositing. To overcome the above problems, several strategies such as the modification of the support and the introduction of additives have been proposed to strengthen the catalytic performance and prolong the robust stability of Pt/Cr-based catalysts. This review firstly gives a brief description of the development of PDH and PDH catalysts. Then, the advanced research progress of supported noble metals and non-noble metals together with metal-free materials for PDH is systematically summarized along with the material design and active origin as well as the existing problems in the development of PDH catalysts. Furthermore, the review also emphasizes advanced synthetic strategies based on novel design of PDH catalysts with improved dehydrogenation activity and stability. Finally, the future challenges and directions of PDH catalysts are provided for the development of their further industrial application.

Spatially isolated cobalt oxide sites derived from MOFs for direct propane dehydrogenation

The "active site isolation" strategy has been proved to be efficient for enhancing the catalytic performance in propane dehydrogenation (PDH). Herein, spatially isolated cobalt oxide sites within nitrogen-doped carbon (NC) layers supported on silicalite-1 zeolite (CoO_x@NC/S-1) were synthesized by a two-step process consisting of the pyrolysis of bimetallic Zn/Co zeolitic imidazole frameworks loaded on silicalite-1 (ZnCo-ZIF/S-1) under N₂ and the subsequent calcination in air atmosphere. This catalyst possesses exceptional catalytic performance for PDH with the propane conversion of 40% and the propene selectivity of >97%, and no apparent deactivation is observed after 10 h PDH reaction at 600 °C. With intensive characterizations and experiments, it is indicated that the real active sites of CoO_x@NC/S-1 are isolated CoO sites during the PDH process. In situ FT-IR spectroscopy shows the same intermediate product (Co-C₃H₇) during both propane dehydrogenation and propene hydrogenation, indicating that they have a reverse reaction process, and a reaction mechanism for PDH is proposed accordingly.

First-principles design of a single-atom–alloy propane dehydrogenation catalyst

Nanoparticles of rhodium dispersed on metal oxides are generally poor catalysts for alkane dehydrogenation because the reactants bind too strongly to the metal. Hannagan et al. performed first-principle calculations indicating that single rhodium atoms in a copper surface should be stable and selective for conversion of propane to propene and hydrogen. Model studies of single rhodium atoms embedded in a copper (111) surface revealed a very high selectivity to propene and high resistance to the formation of surface carbon that would deactivate the catalyst.

Science , abg8389, this issue p. 1444

Coupling of propane with CO2 to propylene over Zn-promoted In/HZSM-5 catalyst

The ZnIn/HZSM-5 catalyst was prepared by the wetness impregnation method, and the structure of catalyst was characterized by XRD, SEM, TEM, H2-TPR, NH3-TPD, XPS, TG, and N2 adsorption–desorption and then investigated in the coupling of propane with CO2 to propylene. It is found that the addition of Zn species is beneficial to the dispersion of In2O3 over HZSM-5, which plays an important role in propene formation, and adjusts the acidity distribution of In/HZSM-5 catalyst, as well as significantly improves the activity of In/HZSM-5 catalyst. The selectivity of propylene is 68.21% in the coupling of propane with CO2 over ZnIn/HZSM-5 catalyst when the time on stream (TOS) is 2 h, reaction temperature is 580 °C, reaction pressure is 0.3 MPa, C3H6:CO2:N2 = 1:4:5, catalyst mass is 0.2 g, and space velocity is 6000 mL gcat−1 h−1. However, the selectivity of propylene is only 63.33% and 0.25% in the propane dehydrogenation or CO2 hydrogenation reaction, respectively. The ZnIn/HZSM-5 catalyst showed a higher stability with only 0.80% conversion drop after three cycles.

Degradation Kinetics of Methyl Orange Dye in Water Using Trimetallic Fe/Cu/Ag Nanoparticles

The release of azo dye contaminants from textile industries into the environment is an issue of major concern. Nanoscale zerovalent iron (nZVI) has been extensively studied in the degradation of azo dye pollutants such as methyl orange (MO). In this study, iron was coupled with copper and silver to make trimetallic Fe/Cu/Ag nanoparticles, in order to enhance the degradation of MO and increase reactivity of the catalyst by delaying the rate of oxidation of iron. The synthesis of the trimetallic nanoparticles (Fe/Cu/Ag) was carried out using the sodium borohydride reduction method. The characterization of the particles was performed using XRD, XPS, EDX, and TEM. The analyses confirmed the successful synthesis of the nanoparticles; the TEM images also showed the desired structures and geometry of the nanoscale zerovalent iron particles. The assessment of the nanoparticles in the degradation of methyl orange showed a notable degradation within few minutes into the reaction. The effect of parameters such as nanoparticle dosage, initial MO concentration, and the solution pH on the degradation of MO using the nanoparticles was investigated. Methyl orange degradation efficiency reached 100% within 1 min into the reaction at a low pH, with lower initial MO concentration and higher nanoparticle dosage. The degradation rate of MO using the nanoparticles followed pseudo first-order kinetics and was greatly influenced by the studied parameters. Additionally, LC-MS technique confirmed the degradation of MO within 1 min and that the degradation occurs through the splitting of the azo bond. The Fe/Cu/Ag trimetallic nanoparticles have proven to be an appropriate and efficient alternative for the treatment of dye wastewater.

Metal-based catalysts for the non-oxidative dehydrogenation of light alkanes to light olefins

This review provides an overview of metal-based catalysts, including Pt-, Pd-, Rh- and Ni-based bimetallic catalysts for non-oxidative dehydrogenation of light alkanes to olefins.

Enormous passivation effects of a surrounding zeolitic framework on Pt clusters for the catalytic dehydrogenation of propane

The significant passivation effect of the zeolitic framework on the catalytic performance of Pt clusters for dehydrogenation of propane to propylene is displayed. Pt/NaX shows 1100% enhanced TOFs and largely improved selectivity compared with Pt@NaX.

Recent progress in heterogeneous metal and metal oxide catalysts for direct dehydrogenation of ethane and propane

Metal and metal oxide catalysts for non-oxidative ethane/propane dehydrogenation are outlined with respect to catalyst synthesis, structure–property relationship and catalytic mechanism.

Tuning partially charged Ptδ+ of atomically dispersed Pt catalysts toward superior propane dehydrogenation performance

An experimentally obtained volcano-type curve is observed for propane dehydrogenation over a group of atomically dispersed Pt catalysts on various supports. The oxidation state of Ptδ+ active sites plays a determining role in enhancing the activity.

One-Step Fabrication of PtSn/γ-Al2O3 Catalysts with La Post-Modification for Propane Dehydrogenation

The catalytic dehydrogenation of propane to propene is an alternative technique to supplement the traditional steam cracking and catalytic cracking process for satisfying the continuously increasing demand for propylene downstream products. In this study, the parent PtSn/γ-Al2O3 catalyst was fabricated via the one-step method for the subsequent La post-modification to prepare the catalysts for propane dehydrogenation. The prepared and spent catalysts were characterized by X-ray diffraction (XRD), N2 adsorption–desorption, scanning electron microscope (SEM), NH3 temperature-programmed desorption (NH3-TPD), H2 temperature-programmed desorption (H2-TPR), and thermogravimetric (TG) analysis. The catalytic performance and characterization results demonstrated that the addition of La into the parent catalyst could significantly improve the catalytic performance of the prepared catalyst. Especially, the PtSn-La2.2 catalyst with the 2.2 wt.% La addition exhibited the stable and highest propylene selectivity (>84%) under the investigation time of 800 min. The introduced La exhibits the ability to adjust the textural properties of the obtained catalysts, curb the acidity of support, promote the reduction of Pt species, and reduce the carbon accumulation on the prepared catalysts.

Effects of phosphorus addition on selectivity and stability of Pd model catalysts during cyclohexene dehydrogenation

P addition to Pd increases dehydrogenation selectivity and increases catalyst stability.

Roles of niobium in the dehydrogenation of propane to propylene over a Pt/Nb-modified Al2O3 catalyst

The application of Pt-based catalysts in propane dehydrogenation (PDH) is restricted by low propylene selectivity, metal sintering and carbon deposition.

A boron nitride nanosheet-supported Pt/Cu cluster as a high-efficiency catalyst for propane dehydrogenation

Here, we report a great promotion in platinum utilization efficiency and catalytic performance for the dehydrogenation of propane using a hexagonal boron nitride nanosheet-supported Pt/Cu cluster catalyst.

Glycerol aerobic oxidation to glyceric acid over Pt/hydrotalcite catalysts at room temperature

Glycerol (GLY) aerobic oxidation in an aqueous solution is one of the most prospective pathways in biomass transformation, where the supported catalysts based on noble metals (mainly Au, Pd, Pt) are most commonly employed. Herein, Pt nanoparticles supported on rehydrated Mg_xAl₁-hydrotalcite (denoted as re-Mg_xAl₁-LDH-Pt) were prepared via impregnation-reduction method followed by an in situ rehydration process, which showed high activity and selectivity towards GLY oxidation to produce glyceric acid (GLYA) at room temperature. The metal-support interfacial structure and catalyst basicity were modulated by changing the Mg/Al molar ratio of the hydrotalcite precursor, and the optimal performance was achieved on re-Mg₆Al₁-LDH-Pt with a GLY conversion of 87.6% and a GLYA yield of 58.6%, which exceeded the traditional activated carbon and oxide supports. A combinative study on structural characterizations (XANES, CO-FTIR spectra, and benzoic acid titration) proves that a higher Mg/Al molar ratio promotes the formation of positively charged Pt^δ+ species at metal-support interface, which accelerates bond cleavage of α-C-H and improves catalytic activity. Moreover, a higher Mg/Al molar ratio provides a stronger basicity of support that contributes to the oxidation of terminal-hydroxyl and thus enhances the selectivity of GLYA. This catalyst with tunable metal-support interaction shows prospective applications toward transformation of biomass-based polyols.