Styrene Selectivity Research Articles

Plastering Sponge with Nanocarbon-Containing Slurry to Construct Mechanically Robust Macroporous Monolithic Catalysts for Direct Dehydrogenation of Ethylbenzene.

Nanocarbons have shown great potential as a sustainable alternative to metal catalysts, but their powder form limits their industrial applications. The preparation of nanocarbon-based monolithic catalysts is a practical approach for overcoming the resulting pressure drop associated with their powder form. In our previous work, a ploycation-mediated approach was used to successfully prepare nanocarbon-containing monoliths. Unfortunately, because there are no macropores in the monolith, it needs to be crashed into millimeter-sized particles before application. Therefore, developing a facile method for preparing mechanically robust nanocarbon-based macroporous monolithic catalysts is vital but still challenging. Herein, evoked by swallows building their nests, we report an approach for successfully preparing a mechanically robust nanodiamond-based macroporous monolith catalyst by plastering melamine sponge (MS) with a slurry composed of nanodiamonds (NDs) and poly(imidazolium-methylene) chloride (PImM) followed by an annealing process. The macroporous monolith catalyst (ND/NCMS-NCPImM) containing NDs well dispersed in N-doped carbon is mechanically robust with enriched macroscopic pores. It exhibits outstanding catalysis toward ethylbenzene to styrene through a direct dehydrogenation reaction with a high styrene rate in a steady state (5.50 mmol g-1 h-1) and high styrene selectivity (99.5%). ND/NCMS-NCPImM shows much higher activity than powder ND by 1.9 fold. In addition, this work solves the significant problem of large pressure drop encountered with conventional powdered nanocarbon catalysts in the flow reactor. This work not only creates an excellent nanodiamond-based macroporous monolithic ethylbenzene direct dehydrogenation catalyst but also presents a promising avenue for preparing other macroporous monolithic catalysts for diverse transformations.

Production of Styrene from Dehydrogenation of Ethylbenzene

AbstractA pseudo‐homogeneous model based on intrinsic rate equations for dehydrogenation of ethylbenzene to styrene in an adiabatic fixed‐bed reactor is developed. Steam and ethylbenzene are the main reactants with styrene as the desired product, and benzene and toluene as by‐products. Styrene production is an endothermic reaction depends on various factors such as temperature, pressure, steam to ethylbenzene ratio, styrene to ethylbenzene ratio in feed. These factors affects the properties like styrene selectivity, ethylbenzene and by‐product conversion etc. The development of the mathematic model includes the application of mass balance, energy balance, and basic thermodynamic relations, momentum balance, Langmuir and Hinshelwood model, Ergun relation, etc. The effects of temperature as well as of the steam‐to‐ethylbenzene and styrene‐to‐ethylbenzene molar ratios in the feed on the selectivity for styrene, ethylbenzene conversion, and conversion to by‐products are also evaluated. The maximum selectivity for styrene can be achieved at increased steam‐to‐ethylbenzene feed ratio and a lower ethylbenzene conversion.

High-Performance Styrene Epoxidation with Vacancy-Defect Cobalt Single-Atom Catalysts.

Exploring highly active and cost-effective catalysts for styrene epoxidation is of great significance, but it remains challenging to simultaneously achieve excellent conversion and selectivity toward styrene oxide. In this work, the structures and performance of Co, Fe, and Cu single-atom catalysts (SACs) in styrene epoxidation with tert-butyl hydroperoxide (TBHP) are predicted using density functional theory (DFT) calculations. The results reveal that the Co-N structure prefers that of styrene oxide over Fe-N and Cu-N structures. This predicted result is verified via catalytic evaluations, where the Co SACs displayed significantly higher styrene oxide selectivity than Fe and Cu SACs. Moreover, the activity of Co SAC can be further improved by the construction of unsaturated vacancy-defect cobalt single sites. As a result, excellent performance with styrene conversion of 99.9% and styrene oxide selectivity of 71% is achieved after a reaction time of 8 h on the optimal Co SAC.

Insight of solvent effect on CeO2 catalyzed oxidation of styrene with tert-butyl hydroperoxide: A combined experimental and theoretical approach

Solvents influence the energetics of adsorbates on the solvent/ catalyst interface and thus control the catalytic activity and product distribution in heterogeneous catalysis. In the present work, influence of different polar organic solvents was studied on the styrene oxidation reaction using TBHP oxidant and CeO2 catalyst. The styrene conversion percentage and selectivity to styrene oxide increased with solvent polarity, while the opposite trend was observed for the other major product, benzaldehyde. Molecular Dynamic (MD) simulation studies were performed to calculate the adsorption energies of the reactant and products on the solvent/ CeO2 interface, together with Density Functional Theoretical (DFT) studies to understand the mechanistic pathway.

Preparation of oxygen reactivity-tuned FeOx/BN catalyst for selectively oxidative dehydrogenation of ethylbenzene to styrene

Oxidative dehydrogenation of ethylbenzene to styrene is considered to be an eco-friendly process, but suffering from overoxidation of the product to carbon oxides due to uncontrollable oxygen reactivity of the catalysts. Here, we report a boron nitride-supported FeOx (FeOx/BN) catalyst, over which an industrially acceptable styrene selectivity (94%) and productivity (0.9 gST gcat−1 h−1) at the conversion of 60% can be attained under oxygen-rich conditions. Based on the investigation of kinetics, CH3OH-TPD, H2-TPR, and O2 pulse reaction, BN support is found to mitigate the oxygen reactivity of FeOx via the strong interaction between the FeOx clusters and the BOx species stemmed from the BN support, which suppresses the overoxidation of ethylbenzene and styrene to carbon oxides. The catalytic tests and structural characterizations reveal that the redox FeOx species initiate the dehydrogenation and then quinone/carbonyl sites on the newly formed coke deposition over FeOx/BN catalyst leads to the increase of activity during the induction period. With the aid of the FeOx and BOx species, the balance between coke deposition and its gasification rates was achieved under oxygen-rich conditions, guaranteeing stable styrene selectivity and productivity.

In situ growth of phosphorus-doped boron nitride on commercial alumina as a robust catalyst for direct dehydrogenation of ethylbenzene

The obtained PBN@Al2O3(N) synthesized by in situ growth of thin PBN layers on commercial Al2O3 exhibited a significantly improved stability with relatively high ethylbenzene conversion and styrene selectivity.

Энергоэффективный одностадийный синтез керамического каталитического конвертера состава [Re,W]/-Al2O3 для дегидрирования этилбензола в стирол

A porous ceramic catalytic converter based on a coarse powder filler α-Al2O3 with an ultrafine strengthening binder of MgO + SiC + SiO2 composition and catalytically active components of Re2O7 and WО3 (up to 4 mass %) was synthesized. Double-sided compaction of the initial mixture at P = 70 to 90 MPa and sintering of the samples at 1200°C to 1400 °C was used. Ceramic catalytic converters with an open porosity of about 40% and a pore size of 0.5 to 1.5 µm were synthesized. Styrene selectivity of about 30% and productivity up to 30 g/(h⋅dm3) in the temperature range from 600 to 700 °С have been experimentally achieved. The degree of catalyst carbonization during the experiment (6 h) did not exceed 0.31 wt. %. A high selectivity for styrene of about 30 % was achieved during the experiments; it was realized in temperature range from 600 to 700 °C. As a result of the research, the scientific basis of a new one-stage technology for obtaining a porous ceramic was developed with simultaneous imparting of catalytic properties. The obtained ceramic catalytic converters can produce styrene with high efficiency and resistance to coke formation in a wide temperature range.

Unraveling high alkene selectivity at full conversion in alkyne hydrogenation over Ni under continuous flow conditions

Carbon dissolution in Ni lattices decreased the interaction of alkenes with the catalyst surface and gave an elusive combination of full phenyl acetylene conversion and high styrene selectivity (92 ± 1%) under continuous flow conditions.

Comparison of NSGA-III with NSGA-II for multi objective optimization of adiabatic styrene reactor

Nature is continuously evolving itself by the different mechanisms so that every aspect of it becomes optimized for different objectives around it. Evolutionary algorithms are developed by mimicking these different mechanisms of evolution. Genetic algorithm is one such evolutionary algorithm. The family of non-dominated sorting genetic algorithms (NSGA) due to its simplicity and efficiency is the most widely used method for solving industrial multi-objective optimization problems. The consideration of elitism in NSGA-II has made it much computationally efficient than NSGA. Recently developed NSGA-III is reported to be more efficient for many-objective (more than two) optimization problems.In this work, the efficacy of NSGA-III is compared with NSGA-II for a three-objective optimization problem of a Styrene reactor. Productivity, Yield and Selectivity of styrene is considered as the three objective functions for the adiabatic styrene reactor. Pareto optimal sets are obtained from both NSGA-II and NSGA-III. The results obtained from NSGA-III shows to provide a more diverse range of optimal operating conditions than NSGA-II.

Revealing the Effect of Mass Transfer on Direct Dehydrogenation of Ethylbenzene Catalyzed by Phosphorous‐doped Boron Nitride: Comparative Study

AbstractPhosphorous‐doped boron nitride (PBN) was previously confirmed to be an effective metal‐free catalyst for the challenging topic of ethylbenzene direct dehydrogenation (DDH) to styrene. Here, the effect of mass transfer factors including the porosity and surface exposure degree of mesoporous‐PBN (m‐PBN) on its performance over DDH was investigated by control experiments. The central pore size of m‐PBN was closely dependent on the thiourea amount and heating rate. The m‐PBN with optimal pore size delivered a significantly improved styrene production rate of 21.47 mmolST g−1 h−1 and styrene selectivity over 98 %. Further, when m‐PBN was in‐situ grown on cordierite, the activity and stability of catalyst could be further enhanced to 27.08 mmolST g−1 h−1 for 50 h stable run, which presented a promising industrial application prospect. This paper justified that the mass transfer factors involved in two‐dimensional metal‐free catalysts were crucial for DDH of ethylbenzene.

A generalized approach to adjust the catalytic activity of borocarbonitride for alkane oxidative dehydrogenation reactions

The borocarbonitrides (BCNs) have exhibited enormous potential as non-metallic catalysts for alkane oxidative dehydrogenation (ODH) reactions. However, the poor electron transportation ability in BCN leads to a low reactivity of oxygen functional groups (CO and BOH). Herein, we present a generalized strategy to promote the catalytic activity of BCN through in situ encapsulation of transition-metal (Fe, Co, Ni) nanoparticles within BCN nanotubes (BCNNTs). Among them, individual metal particles themselves do not contribute directly on ODH reactions and mainly serve as electron modulators to tune the electron density of CO and BOH active sites on BCNNTs. As a result, catalytic activities of all metal@BCNNTs catalysts surpass pure BCN in ethylbenzene (EB) ODH reactions, among which Fe@BCNNTs displays a significant activity enhancement with 36 % EB conversion with the styrene (ST) selectivity remaining >98% under gentle reaction conditions. Structural and kinetic analyses proved that the promotion effect originated from the strong interactions between metal nanoparticles and BCNNTs. The theoretical calculations disclosed that the enhanced ODH activity was due to the electron transfer from the encapsulated metal to BCNNTs, which increases the electron transportation ability and electron density of BCNNTs, thus promoting the nucleophilicity of CO and BOH active sites, leading to the reduced activation energy barrier for CH bond dissociation. The present work sets forth the structure-function relationship, identifying opportunities for rational design of highly efficient BCN catalysts for ODH reactions.

Interfacial Electronic Effects in Co@N-Doped Carbon Shells Heterojunction Catalyst for Semi-Hydrogenation of Phenylacetylene.

Metal-supported catalyst with high activity and relatively simple preparation method is given priority to industrial production. In this work, this study reported an easily accessible synthesis strategy to prepare Mott-Schottky-type N-doped carbon encapsulated metallic Co (Co@Np+gC) catalyst by high-temperature pyrolysis method in which carbon nitride (g-C3N4) and dopamine were used as support and nitrogen source. The prepared Co@Np+gC presented a Mott-Schottky effect; that is, a strong electronic interaction of metallic Co and N-doped carbon shell was constructed to lead to the generation of Mott-Schottky contact. The metallic Co, due to high work function as compared to that of N-doped carbon, transferred electrons to the N-doped outer shell, forming a new contact interface. In this interface area, the positive and negative charges were redistributed, and the catalytic hydrogenation mainly occurred in the area of active charges. The Co@Np+gC catalyst showed excellent catalytic activity in the hydrogenation of phenylacetylene to styrene, and the selectivity of styrene reached 82.4%, much higher than those of reference catalysts. The reason for the promoted semi-hydrogenation of phenylacetylene was attributed to the electron transfer of metallic Co, as it was caused by N doping on carbon.

Catalytic oxidation of styrene and its reaction mechanism consideration over bimetal modified phosphotungstates

Cobalt and nickel modified phospotungstates (CoNiPW) were fabricated via the reaction of H3PW12O40•6•5H2O (PW) with Co(NO3)2•6H2O and NiCl•6H2O, followed by calcination; and then characterized by various physicochemical techniques, such as XRD, FT-IR, UV–vis, SEM, TEM and XPS to determine the surface morphology, structure and composition. The as-prepared CoNiPW was used as a catalyst for solvent-free oxidation of styrene with molecular oxygen oxidant. It exhibited efficient in achieving higher conversion of styrene and high selectivity to benzaldehyde. A detail study on influence of key reaction parameters, as well as catalytic role of various constituents in CoNiPW on the reactivity and selectivity was conducted to identify active sites. The reaction mechanism via benzyl alcohol intermediate was proposed by in situ adsorption of styrene on the catalyst surface and the product intermediate produced in the oxidation reaction. The recovery and reusability of the catalyst was also evaluated.

Catalytically active nano-porous cobalt-palladium alloys

The potential advantages of nano-alloys and particularly, nano-porous alloys, place them at the "spotlight" of heterogeneous catalysis. Nevertheless, controlling the precise compositions of these materials is still a synthetic challenge. Previous research introduced the fabrication of metals and alloys with a high nano-scale porosity and controllable compositions, via a hydrogen-mediated chemical reduction process of metal complex salts. We have used this procedure to obtain two magnetic nano-porous Co-Pd alloys, pure porous palladium and pure porous cobalt. Single crystal X-ray diffraction studies enabled structural determination of the two Co-Pd bi-complex salts that were used as precursors for these alloys. Powder X-ray diffraction studies determined the crystalline phases of the alloys and indicated the nanometric size of their crystallites. High-resolution scanning electron microscopy indicated that these alloys assemble as highly porous clusters of interconnected nano-crystallites. It also indicated that each alloy cluster preserves the micrometric morphologies of its salt precursor. Energy dispersive X-ray spectroscopy showed that the alloys exhibit uniform composition down to the micro-level, which preserved the Co/Pd ratio within the salts. Focused ion beam tomography enabled 3D structural representation of the alloys and metals. Geometrical analysis of the 3D reconstructed data determined 90% porosity and a specific surface area of ~100 m2/g for the alloys. In addition, the alloys showed improved catalytic activity in the semi-hydrogenation of phenylacetylene, compared to the pure metals and commercial Pd/C. Moreover, their magnetic properties enabled facile recovery at the end of the reaction. The yield for styrene in this reaction was increased using "design of experiments" (DOE), a method for optimization of reaction conditions. Furthermore, our experiments implied that a highly porous structure significantly improves the selectivity of styrene in the reaction. These results demonstrated the advantage of fabricating nano-porous alloys with uniform compositions that may exhibit special properties and serve as new and efficient catalysts.

Efficient organocatalytic synthesis of styrene oxide from styrene and its kinetic study in a continuous-flow microreaction system

Alkene epoxidation, which consists an important reaction in the synthesis of various fundamental chemical compounds, has aroused increasing attention in the field of organic synthesis. Hydrogen peroxide that is often considered as a green oxidant for the epoxidation of olefins is relatively unstable when reacting in batch reactor. Microreactor system possesses the advantages of high mass and heat transfer performances as well as great controllability, making it a suitable pathway for the epoxidation of olefins. In this work, a highly efficient microreaction system for epoxidation of styrene is studied. Both high conversion of styrene and excellent product selectivity could be achieved. The effects of temperature, residence time, molar fraction of catalyst, molar ratio of MeCN/t-BuOH, flow rate of H2O2 and buffer solution were studied. According to the experiment data, kinetic equation was built, which will be in favor of verifying the rationality of the reaction mechanism and optimizing experimental conditions.

A Highly Selective Metal‐Free Boron‐Based Catalyst for Oxidative Dehydrogenation of Ethylbenzene

Main observation and conclusionOxidative dehydrogenation of ethylbenzene is considered as an alternative route to styrene because of its exothermic and irreversible reaction nature, but encounters low styrene selectivity due to the deep‐oxidation over metal oxide‐based catalysts. Herein, we reported that a metal‐free boron‐based catalyst consisting of boron phosphate and boron nitride (BPO4/BN) exhibited high activity and selectivity in oxidative dehydrogenation of ethylbenzene to styrene. High selectivity of styrene (95.1%) was achieved at 27.7% ethylbenzene conversion level over the optimized BPO4/BN catalyst. The tetra‐coordinated boron (BO4) species of BPO4 was speculated to be responsible for the ODH of ethylbenzene, and a synergistic effect between BPO4 and BN can remarkably improve the catalytic performance of the BPO4/BN catalyst. The optimized BPO4/BN catalyst showed a higher styrene formation rate of 4.0 mmol gcat−1·h−1, compared individually to BPO4 (2.8 mmol·gcat–1·h–1) and BN (0.5 mmol·gcat–1·h–1).

A Top‐Down Strategy to Realize Surface Reconstruction of Small‐Sized Platinum‐Based Nanoparticles for Selective Hydrogenation

AbstractOver the past decades, despite the substantial efforts that have been devoted to the modifications of Pt nanoparticles (NPs) to tailor their selectivities for hydrogenation reactions, there are still a lack of facile strategies for precisely regulation of the surface properties of NPs, especially for those with small sizes. In this work, we propose a top‐down thermal annealing strategy for tuning the surface properties of Pt‐based NPs (≈4 nm) without the occurrence of aggregation. Compared to conventional bottom‐up methods, the present top‐down strategy can precisely regulate the surface compositions of Pt‐Cd NPs and other ternary Pt‐Cd‐M NPs (M=Fe, Ni, Co, Mn, and Sn). The optimized Pt‐Cd NPs exhibit excellent selectivity toward phenylacetylene and 4‐nitrostyrene hydrogenations with a styrene selectivity and 4‐aminophenyl styrene selectivity of 95.2 % and 94.5 %, respectively. This work provides a general strategy for the surface reconstructions of Pt‐based NPs, and promotes fundamental research on catalyst design for heterogeneous catalysis.

A Top-Down Strategy to Realize Surface Reconstruction of Small-Sized Platinum-Based Nanoparticles for Selective Hydrogenation.

Over the past decades, despite the substantial efforts that have been devoted to the modifications of Pt nanoparticles (NPs) to tailor their selectivities for hydrogenation reactions, there are still a lack of facile strategies for precisely regulation of the surface properties of NPs, especially for those with small sizes. In this work, we propose a top-down thermal annealing strategy for tuning the surface properties of Pt-based NPs (≈4 nm) without the occurrence of aggregation. Compared to conventional bottom-up methods, the present top-down strategy can precisely regulate the surface compositions of Pt-Cd NPs and other ternary Pt-Cd-M NPs (M=Fe, Ni, Co, Mn, and Sn). The optimized Pt-Cd NPs exhibit excellent selectivity toward phenylacetylene and 4-nitrostyrene hydrogenations with a styrene selectivity and 4-aminophenyl styrene selectivity of 95.2 % and 94.5 %, respectively. This work provides a general strategy for the surface reconstructions of Pt-based NPs, and promotes fundamental research on catalyst design for heterogeneous catalysis.

Coproduction of styrene and benzaldehyde over a boron nitride-supported monomeric MoOx catalyst

Styrene and benzaldehyde are manufactured by energy-intensive direct dehydrogenation and an intermittent liquid chlorine oxidation batch process, respectively. The coproduction of styrene and benzaldehyde through selective oxidation of ethylbenzene is an environmentally friendly and economically feasible alternative. However, it is hard to control the selectivity for styrene or benzaldehyde as a result of deep oxidation reactions. Here, we report an efficient selective oxidation catalyst, boron nitride-supported monomeric MoOx (MoOx/BN), over which styrene and benzaldehyde can be selectively coproduced. Structure characterization and catalytic evaluation reveal that the MoOx/BN catalyst is conducive to the generation of benzaldehyde and less formation of COx than for monomeric MoOx supported on inert silica. Based on the kinetic analysis, over MoOx/BN catalyst, styrene is the primary product and benzaldehyde is the major by-product in the subsequent oxidation reaction. The boron hydroxy groups of the MoOx/BN catalyst are involved in the reaction network, which could regulate the reaction behavior of monomeric MoOx species; thus the reaction generates more benzaldehyde.

Simulation and optimization of axial-flow and radial-flow reactors for dehydrogenation of ethylbenzene into styrene based on a heterogeneous kinetic model

In this study, steady-state axial-flow and radial-flow multibed catalyst reactors for dehydrogenation of ethylbenzene into styrene were simulated based on an intrinsic heterogeneous kinetic model. The reactors were then optimized using nonlinear programming with the multiobjective function of maximizing styrene selectivity and conversion. The simulations were consistent and versatile. Comparing the two optimized reactor configurations, radial-flow has proved to be a better alternative than axial-flow because of operating at lower pressures. The benefits of operating at lower pressures are also evident at optimized inlet temperature schemes, as the inlet temperatures of catalyst beds are greater along reactor pressure drop. The obtained set of optimal results can be used to perform an integrated process analysis and define suitable operational conditions. Weighing objective functions with respectively 0.3 and 0.7, styrene selectivity and conversion were respectively 85.3% and 72.5% for the axial-flow reactor and 87.0% and 76.5% for the radial-flow reactor.