Styrene Rate Research Articles

Tailored Pd/C bifunctional catalysts for styrene production under an ethylbenzene oxidative dehydrogenation assisted direct dehydrogenation scheme

Rational design of efficient ethylbenzene (EB) dehydrogenation catalyst and reaction route is the key scientific challenge for styrene (ST) formation. We reported here a dual-path dehydrogenation (DPDH) route to efficiently convert EB to ST on a Pd/hollow nanocarbon spheres bifunctional catalyst, which exhibited ST formation rate up to 7.11 mmol g−1 h−1 with > 99 % selectivity. Detailed kinetic, isotopic and surface reaction analysis and corresponding DFT calculation suggested that the relatively high intrinsic catalytic activity originated not only from the single atomically dispersed Pd-based coordination structure but also the unique oxidative dehydrogenation (ODH) assisted direct dehydrogenation (DDH) reaction route. In this route, the small amount of H2O produced from ODH effectively lowered the energy barrier for hydrogen generation/desorption via a proton transfer process promoting the DDH process. The present work shed light on the rational design of catalyst and routes for highly efficient alkane dehydrogenation reaction systems.

Three‐Dimensional Interconnected Porous Nitrogen‐Doped Carbon Hybrid Foam for Notably Promoted Direct Dehydrogenation of Ethylbenzene to Styrene

AbstractOwning to the high corrosion‐resistance, stable structure, unique surface properties and sustainability, the carbon‐base catalysts have attracted increasing interest in heterogeneous catalysis. Herein, we report a facile combining strategy to fabricate a novel three‐dimensional (3D) interconnected porous nitrogen‐doped carbon hybrid foam featuring with the interconnected nitrogen‐doped carbon foam coated by porous nitrogen‐doped carbon (NCMS@NCGlu‐NH4Cl) by annealing the freeze‐dried NH4Cl‐glucose containing aqueous solution soaked melamine sponge (MS@Glu/NH4Cl). The as‐prepared NCMS@NCGlu‐NH4Cl hybrid foam shows 1.6 times high steady‐state styrene rate (4.77 mmol g−1 h−1) with 96.4 % of selectivity for direct dehydrogenation of ethylbenzene to styrene as compared to the well‐established nanodiamond. This work not only generates an excellent carbon catalyst to replace the established nanodiamond for direct dehydrogenation of ethylbenzene, but also opens up a potential avenue for designing novel carbon materials towards the adsorption and supercapacitor besides acting as a promising catalyst for diverse transformations.

Structure-performance relationship of nanodiamonds @ nitrogen-doped mesoporous carbon in the direct dehydrogenation of ethylbenzene

Nanocarbon materials have been reported as an alternative robust metal-free catalyst in the field of the catalytic dehydrogenation with improved catalytic performance as well as stability. In this study, the hybrid metal-free catalyst consisting of dispersed nanodiamonds within a nitrogen-doped mesoporous carbon (ND@NMC) phase was investigated. Such material with high effective surface area and porosity was prepared under different thermal treatment temperatures and further evaluated for the direct dehydrogenation (DDH) of ethylbenzene (EB) to styrene (ST). The characterization techniques such as N2 adsorption-desorption, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy and Raman spectroscopic analysis were used to investigate the surface properties and structures of the as-prepared ND@NMC composites. The ND@NMC-700 catalyst annealed at 700°C presented a ST specific reaction rate and a relative areal activity of 5.8mmolST gcatalyst−1h−1 and 0.28μmolST m−2h−1 with a ST selectivity of 99.6%, which is the highest DDH activity among the investigated nanocarbons including ND, carbon nanotubes, NMC and ND@MC (ND covered by mesoporous carbon) catalysts. The superior dehydrogenation performance could be attributed to the high dispersion of the metal-free nanodiamond centers within the NMC layer which provided a well surface contact with the reactant. It can also be confirmed that the rational contents of ketone (CO) functional groups, as well as the opened porous network in ND@NMC-700 catalyst resulted to the superior DDH activity and styrene selectivity. Moreover, the presented nitrogen groups are beneficial for construction of surface defects and porosity as well as the improvement of styrene selectivity.

Macroscopically shaped monolith of nanodiamonds @ nitrogen-enriched mesoporous carbon decorated SiC as a superior metal-free catalyst for the styrene production

Nanodiamonds (NDs) are recognized as a class of robust metal-free catalysts for the steam-free, direct dehydrogenation (DDH) of ethylbenzene (EB) to styrene (ST). In spite of that, some main drawbacks, such as their powdery form along with their tendency to form aggregates, limit their full exploitation at the industrial level. In this work, we describe the preparation of macroscopically shaped monoliths consisting of silicon carbide-based foams coated with a nitrogen-rich mesoporous carbon matrix (NMC) as a non-innocent glue for highly dispersed ND fillers. The NMC phase is prepared from cheap and non-toxic food-grade components and it prevents the undesired NDs agglomeration thus maximizing the reagents exposure throughout the catalytic DDH tests. Moreover, the NMC phase represents a key source of surface basicity capable of inhibiting the occurrence of EB cracking side reactions during the catalytic runs. As a result, the ND@NMC/SiC composite shows excellent dehydrogenation performance already at low ND loading if compared with the powdery NDs and/or the SiC-supported NDs of the state-of-the-art. Noteworthy, the ND@NMC/SiC composite presents its best catalytic performance under DDH conditions close to those used in industrial plants (reaction temperture up to 600°C and EB concentrations up to 10 vol.%) with high ST rates (λcatal. of 9.9mmolSTgcat−1h−1), ST selectivity over 96% and long term stability on stream.

Efficient tuning of microstructure and surface chemistry of nanocarbon catalysts for ethylbenzene direct dehydrogenation

A facile and scalable approach to efficiently tune microstructure and surface chemical properties of N‐doped carbocatalysts through the controlled glucose hydrothermal treatment with diverse parameters and subsequent pyrolysis of pretreated carbonaceous materials with melamine (GHT‐PCM) was presented. Various characterization techniques including high resolution transmission electron microscopy (HRTEM), N2 adsorption desorption (BET), X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), Raman spectroscopy (Raman), and fourier transform infrared spectroscopy (FTIR) were employed to investigate the effect of prior GHT on the microstructure and surface chemical properties of N‐doped carbocatalysts, as well as to reveal the relationship between catalyst nature and catalytic performance in oxidant‐ and steam‐free direct dehydrogenation (DDH) of ethylbenzene for styrene production. It was found that the GHT process and its conditions significantly affect microstructure and surface chemical properties of the N‐doped carbocatalysts, which subsequently influences their catalytic performance in DDH reaction dramatically. Interestingly, the prior GHT can remove the carbon nitride layer formed on parent nanocarbon in the process of melamine pyrolysis, produce structural defects, and tune surface element component, through the “detonation” of polysaccharide coating on nanocarbon. The as‐prepared N‐doped CNT (M‐Glu‐CNT) by the established GHT‐PCM approach demonstrates higher catalytic performance (4.6 mmol g−1h−1 styrene rate with 98% selectivity) to the common N‐doped CNT (M‐CNT, 3.4 mmol g−1 h−1 styrene rate with 98.2% selectivity) as well as to pristine CNT (2.8 mmol g−1 h−1 styrene rate with 96.8% selectivity), mainly ascribed to increased structural defects, enriched surface ketonic CO groups, and improved basic properties from N‐doping on the M‐Glu‐CNT, those strongly depend on GHT conditions. The excellent catalytic performance of the developed M‐Glu‐CNT catalyst endows it with great potential for future clean production of styrene via oxidant‐ and steam‐free conditions. Moreover, the directed GHT‐PCM strategy can be extended to the other N‐doped carbonaceous materials with enhanced catalytic performance in diverse reactions by tuning their microstructure and surface chemistry. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2543–2561, 2015