Selectivity Of Main Products Research Articles

MxOy-ZrO2 (M = Zn, Co, Cu) Solid Solutions Derived from Schiff Base-Bridged UiO-66 Composites as High-Performance Catalysts for CO2 Hydrogenation.

Metal-organic frameworks have been exploited as excellent solid precursors and templates for the preparation integrated nanocatalysts with multicomponent and hierarchical structures. Herein, a novel synthetic protocol has been developed to fabricate versatile Zr-based solid solutions (such as ZnO-ZrO2, Co3O4-ZrO2, and CuO-ZrO2) via pyrolysis of Schiff base-modified UiO-66 octahedrons (size <100 nm), which were then utilized as efficient catalysts for CO2 hydrogenation. The Schiff base serves as an effective bridge to dope secondary metal ions into UiO-66 frameworks with controlled amounts of 0.13-8.8 wt %, which are initially hard to achieve. Interestingly, by simply changing the loading metal ions, the selectivity of C1 hydrogenation products can be facilely tuned. For instance, the maximum CO2 conversion of ZnO-ZrO2, Co3O4-ZrO2, and CuO-ZrO2 solid solutions were 5.8, 11.4, and 22.5%, with the main product selectivity of 70% CH3OH, 92.5% CH4, and 86.7% CO, respectively. Moreover, in situ diffuse reflectance infrared Fourier transform spectra characterization reveals that the significant difference in C1 product selectivity is mainly determined by the balance of *HCOO, *CH3O, and *CO intermediate species over the Zr-based solid solutions.

Surface Modification on Pd Nanostructures for Selective Styrene Oxidation with Molecular Oxygen

AbstractThe catalytic oxidation based on molecular oxygen (O2) is one of the most preferable choices for oxidation reactions toward atom‐efficient utilization of oxidants, in which heterogeneous catalysts based on palladium (Pd) nanostructures have been commonly used. However, in terms of selective styrene oxidation, it is still a great challenge to balance reactivity and selectivity by employing pure Pd catalysts. Herein, a well‐designed model for seeking a selective oxidation catalyst based on surface lattice engineering is described. In the proposed model, Au atoms are sparsely deposited on the surface of concave Pd nanostructures. As such, the activation degree of adsorbed O2 can be altered by simply tailoring the concentration of Au atoms on surface, suppressing the formation of over‐oxidized byproducts. Moreover, the Pd@Au nanostructures reported here have sufficient plasmonic cross‐sections for light harvesting, which enables light‐driven catalysis through a photothermal effect. Taken together, the Pd@Au0.08 concave nanostructures with an Au/Pd ratio of 8% achieve 87% main product selectivity with a conversion of 44% in the aerobic oxidation of styrene using molecular O2 (1 atm) without additional initiator.

친환경 냉매 제조를 위한 오불화프로펜 수소화반응에 대한 예측

친환경 냉매인 R-1234yf를 제조하기 위하여 오불화프로펜인 1,2,3,3,3-pentafluoropropene의 수소화반응을 수행하였다. 수소화반응 촉매로 팔라듐이 담지된 탄소입자를 제조하여 실험에 사용하였다. 반응조건에 따른 수소화반응 활성을 규명하기 위하여 WHSV, 반응온도 및 반응물의 조성에 따른 반응성능에 대하여 조사하였다. 일정한 실험 조건에서 WHSV는 주 생성물의 선택도에 영향이 없으며, 반응온도의 경우 높은 온도에서 우수한 생성물 선택도를 보였다. 수소와 반응물의 비의 경우 1.5 미만에서 우수한 생성물 선택도를 보였다. 또한 반응조건에 따른 생성물의 수율을 예측할 수 있는 모델식을 통계학적 접근을 통해 완성하였다. In this study, hydrogenation of 1,2,3,3,3-pentafluoropropene was performed to produce R-1234yf as an environmentally friendly refrigerant. Palladium based carbon was prepared as a catalyst in the hydrogenation reaction. The effect of reaction conditions including the weight hourly space velocity (WHSV), reaction temperature and ratio of hydrogen and reactants on the catalytic performance was investigated. Under the identical reaction conditions, the effect of WHSV on the main product selectivity was insignificant, but a high reaction temperature was essential for the good product selectivity. A high product selectivity was also obtained when the ratio of hydrogen and reactants kept less than 1.5. Moreover, a correlation model involving the statistical approach to predict product yields was developed.

Strategy for Scaling‐up of a Microsieve Dispersion Reactor

AbstractFor the application of microreactors in industrial processes, more scaling‐up strategies are still required except of the original concept, the numbering‐up. A more maneuverable and economic approach, combining both similarity‐up and numbering‐up, is introduced as an example for an innovative strategy. CFD simulation is also applied to assist analysis and optimization of fluid distribution. Based on this concept, named similarity‐up + numbering‐up + simulation, a pilot‐plant microsieve dispersion minireactor used to proceed the reaction of cyclohexanecarboxylic acid and oleum is designed and tested experimentally. With the contribution of similarity‐up, the treating capacity of the core unit is significantly increased. Ten parallel units are integrated to form a correspondingly enhanced capacity of the microreactor which exhibits low pressure drop, stable operating performance, and excellent main product selectivity.

Tunable Metal/Silicon Hybrid Dots Catalysts for Hydrocarbon Selective Oxidation

Metal (Au, Ag, and Pt)/silicon hybrid dots were facially prepared by a one-step reaction between Si quantum dots (SiQDs) and metal salts at room temperature without any templates and surfactants. The obtained Au/SiQDs were demonstrated to be a superior catalyst for selective oxidation of cyclohexene. By altering the composition of Au/SiQDs catalysts, the selectivity of main products can be tuned step-by-step.

Kinetics research on fast exothermic reaction between cyclohexanecarboxylic acid and oleum in microreactor

Microreactors are effective tools for the intensification of fast exothermic chemical reactions. In this work, we focus on the kinetics study of a microreacting process to provide a deeper understanding of the transport and reaction performance within microreactors. An experimental setup incorporating an online kinetic measurement method was developed based on the temperature–conversion relationship in the cyclohexanecarboxylic acid–oleum reaction – a crucial reaction for the preparation of ɛ-caprolactam. The reactant conversion was successfully recorded in a reaction time of less than 1.0 s, and it was determined that the reaction rate was mainly controlled by the mixing of reactants. The mass transfer coefficient in the microreactor reached 10 −4 m/s, and the observed selectivity of the main-product was higher than 97%. Based on the experimental results, a single-droplet model was developed to establish a better understanding of the temperature and concentration distributions in the reacting system as well as analyze the effect of drop size on main-product selectivity.

Attempts To Improve the Product Slate Quality: Influence of Coke-on-Catalyst Content

Several catalysts with increasing initial coke content were processed in the Microdowner unit in order to assess the activity and selectivity of coked catalyst. Tests were carried out at both constant operating conditions and changing catalyst-to-oil ratio to maintain conversion. It was found that coke on regenerated catalyst (CRC) has very little influence on the main product selectivity, while some effect on product quality was detected. CRC changed the hydrogen transfer to cracking relative rate as it lowered site density, resulting in a dramatic increase in the isobutene-to-isobutane ratio. Gasoline was more olefinic and less paraffinic, while sulfur content increased. LCO yield increased slightly, producing a distillate with better quality (fewer aromatics and more paraffins). When ZSM5 is used, it has been observed that propylene selectivity increases at constant conversion at a rate around 1 point of propylene per percent coke on catalyst. Apart from the cracking selectivity changes in the riser, the significant increase in catalyst circulation that is necessary to maintain conversion may have some beneficial effects for feed vaporization and reduced thermal cracking at the injection point.

Hydrogenation of p-chloronitrobenzene on Ni–B Nanometal Catalysts

A series of Ni–B catalysts were prepared by mixing nickel acetate in 50% ethanol/water or methanol/water solution. The solution of sodium borohydride (1 M) in excess amount to nickel was then added dropwise into the mixture to ensure full reduction of nickel cations. The mol ratio of boron to nickel in mother solution was 3 to 1. The effects of preparation conditions such as temperature, stirring speed, and sheltering gas on the particle size, surface compositions, electronic states of surface atoms and catalytic activities of the Ni–B catalysts were studied. Ranel nickel catalyst was included for comparison. These catalysts were characterized by N2 sorption, X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. The catalysts were tested for liquid phase hydrogenation of p-chloronitrobenzene. All of the catalysts prepared in this study had nanosized particles. The preparation condition has significant influence on the particle size and surface compositions of the catalyst. The Ni–B catalyst was passivated by boron; therefore it was more stable than Raney nickel and did not catch fire after exposure to air. The catalysts prepared under N2 flow could suppress the oxidation of Ni by the dissolved oxygen in water and had metallic state of nickel. The catalyst prepared with vigorous stirring at 25°C under N2 stream yielded the smallest particles and resulted in the highest activity. It was much more active than the Raney nickel catalyst. The reaction condition also has pronounced effect on the hydrogenation activity. Using methanol as the reaction solvent increased p-chloronitrobenzene conversion to a large extent, compared to that using ethanol as the reaction medium. The selectivity of main product (p-chloroaniline) was greater than 99% on all of the Ni–B catalysts.

Mathematical modeling and simulation for gas–liquid reactors

Gas–liquid reactors are widely used in many industrial processes such as oxidation, hydroformylation, chlorination, etc. The paper develops comprehensive model for reactors using the mixing cell approach. It incorporates heat and mass transfer effects in the film and uses a boundary element method to solve the film model equations. The fluxes obtained at the interface are then directly used as the link to the reactor model. Simple isothermal and non-isothermal reactions were numerically tested. Application to two industrially important case studies, chlorination of butanoic acid and oxidation of cyclohexane are briefly illustrated. For the autocatalytic chlorination of butanoic acid, the yield of desired product, monochlorobutanoic acid, is favored by the high degree of mixing in the liquid phase. Therefore, this reaction should be carried out in a CSTR. A series of five bubble tanks with parallel gas reactant feed for cyclohexane oxidation was also simulated. It was found that the cyclohexane conversion is low while the oxygen conversion is relatively high and almost constant in each tank. Due to the complex multistep nature of this reaction scheme, oxygen is consumed in many steps of oxidation and selectivity of main products (which are intermediate products in the reaction scheme) depends on the critical control of over-oxidation in the kinetic mechanism.