Hongfang Ma

Effects of Zr and K Promoters on Precipitated Iron-Based Catalysts for Fischer–Tropsch Synthesis

The effects of Zr and K promoters on the structure, adsorption, reduction, carburization and catalytic behavior of precipitated iron-based Fischer–Tropsch synthesis (FTS) catalysts were investigated. The catalysts were characterized by N2 physisorption, temperature-programmed reduction/desorption (TPR/TPD) and Mössbauer effect spectroscopy (MES) techniques. As revealed by N2 physisorption, Zr and/or K promoted catalysts showed lower surface area than Fe/SiO2 catalyst. Zr promoter inhibited the reduction and carburization because of the interaction between Fe and Zr in Fe–Zr/SiO2 catalysts. K promoter enhanced the reduction in CO and apparently facilitated the CO adsorption, thus promoted the carburization, but it retarded the reduction in H2 and severely suppressed the H2 adsorption. Compared with the singly promoted catalysts, the doubly promoted catalyst had the highest FTS activity. In addition, both Zr and K promoters suppressed the formation of methane and shifted the production distribution to heavy hydrocarbons.Graphical AbstractBoth Zr and K restrained the formation of methane, and increased the heavy hydrocarbons selectivity. In the FTS reaction, the doubly promoted catalyst Fe–Zr–K/SiO2 had the highest FTS activity.

Effect of Sn Addition in Gas Phase Hydrogenation of Acetic Acid on Alumina Supported PtSn Catalysts

Alumina supported Pt, Sn and PtSn catalysts were prepared by impregnation and tested in the gas phase hydrogenation of acetic acid, and characterized by N2-physisorption, XRD, H2-TPR, H2-pulse chemisorption, H2-TPD, DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy), XPS, electron microscopy techniques (TEM, HRTEM and EDX). Results show that Sn addition to Pt/Al2O3 catalyst can improve the conversion of acetic acid and suppress the production of by-products, as well as enhance the selectivity towards ethanol. The optimization of activity and selectivity can be achieved by changing reaction temperature and pressure. Characterizations indicated that the better performance of PtSn/Al2O3 catalyst is due to the formation of PtSn alloy and Pt-SnOx species.Graphical Abstract

Effect of boron on ZSM-5 catalyst for methanol to propylene conversion

Abstract B-ZSM-5 catalysts were prepared by various modification methods with boric acid, including ion-exchange, impregnation and direct synthesis. The catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), NH3-Temperature Programmed Desorption (NH3-TPD), N2 adsorption-desorption, Fourier Transform Infrared spectrometry (FT-IR), 27Al and 11B MAS NMR spectra. The results revealed that the weak acidity of catalysts was significantly increased by modification. The catalytic activity was measured in a fixed bed at 460°C for methanol to propylene (MTP) reaction. The results of MTP reaction showed a great increment of the propylene selectivity for the boron modified samples, especially for the directly synthesized B-ZSM-5 which also displayed high activity and selectivity towards C2 =-C4 = olefins. It was found that the remarkable selectivity strongly depended on the intensity of weak acidity.

Process simulation of dimethyl ether synthesis via methanol vapor phase dehydration

The production processes included catalytic dehydration of methanol in an adiabatic fixed-bed reactor and two columns product separations. In this study, the technological process for dimethyl ether (DME) synthesis is built on PRO/II platform based on the combined parameters of the reaction dynamic model for methanol dehydration reaction, the improved NRTL model of the liquid phase, the PR model of vapor phase. In order to validate the proposed model, the simulation results have been compared with the available data from a set of industrial production equipment with a production capacity of 200 000 tonnes per annum. A comparison between the calculated and measured results has proved that these results are satisfactory. The bed height and the volume of the catalytic bed are calculated aim at one million t/a DME yields and while taking account of high-purity DME production. After discussing the influence of feed stage location and reflux ratio for DME product purity, the suitable unit operation conditions are chosen. Accordingly, accurate process simulation results provide the basis and guidance for an improvement and development of the similar industrial device.

La and Mn Promotion of Ni/Al2O3 Catalysts for Syngas Methanation

24Ni-2La, 24Ni-2Mn, and 24Ni-2La-2Mn catalysts were prepared by co-impregnation method for syngas methanation, and were characterized by N2 adsorption-desorption, XRD, H2-TPR, and TEM. The addition of La and/or Mn as promoters can decrease the crystal size of Ni particles and prevent the growth of Ni particles during calcination and reduction. 24Ni-2La, 24Ni-2Mn, and 24Ni-2La-2Mn have similar average Ni particle size, which is in the range of 12.8–13.2 nm. For syngas methanation, 24Ni-2La presents a better synergism effect than both 24Ni-2Mn and 24Ni-2La-2Mn.

Highly selective production of heavy hydrocarbons over cobalt–graphene–silica nanocomposite catalysts

Herein, cobalt–graphene–silica nanocomposites were prepared by a sol–gel method to produce heavy hydrocarbons for Fischer–Tropsch synthesis. The catalysts were characterized by N2 physisorption, XRD, TEM, TPR, TPD, XPS, and DRIFTS techniques. The activity of catalysts and the selectivity of products were examined in a tubular fixed-bed reactor. It can be concluded that the introduction of graphene into cobalt–silica nanocomposites significantly enhanced the amount and stability of adsorbed CO at low temperatures, resulting in higher concentrations of CO species on the catalyst surface. Moreover, graphene can weaken the cobalt–silica interaction, leading to higher degree of reduction of cobalt oxides and higher adsorption amounts of H2. In addition, the introduction of graphene led to the formation of cobalt with smaller particle sizes, which contributed to great enhancement of CO conversion. The selectivity to methane distinctly decreased to 4.2% from 8.1%, whereas the selectivity to C5+ products increased from 84.5% to 92.4%. The α value increased from 0.89 for the Co–Si catalyst to 0.94 for the Co–0.1GSi catalyst. In addition, with the increase in the graphene content, the fraction of heavy hydrocarbons (C19–29) for catalysts evidently increased to 36.0% from 28.3%, but the fraction of naphtha (C5–12) clearly reduced to 17.7% from 27.7%.

Study on Effective Radial Thermal Conductivity of Gas Flow through a Methanol Reactor

Abstract The heat conduction performance of the methanol synthesis reactor is significant for the development of large-scale methanol production. The present work has measured the temperature distribution in the fixed bed at air volumetric flow rate 2.4–7 m3 · h−1, inlet air temperature 160–200°C and heating tube temperature 210–270°C. The effective radial thermal conductivity and effective wall heat transfer coefficient were derived based on the steady-state measurements and the two-dimensional heat transfer model. A correlation was proposed based on the experimental data, which related well the Nusselt number and the effective radial thermal conductivity to the particle Reynolds number ranging from 59.2 to 175.8. The heat transfer model combined with the correlation was used to calculate the temperature profiles. A comparison with the predicated temperature and the measurements was illustrated and the results showed that the predication agreed very well with the experimental results. All the absolute values of the relative errors were less than 10%, and the model was verified by experiments. Comparing the correlations of both this work with previously published showed that there are considerable discrepancies among them due to different experimental conditions. The influence of the particle Reynolds number on the temperature distribution inside the bed was also discussed and it was shown that improving particle Reynolds number contributed to enhance heat transfer in the fixed bed.

Impact of heating rate and solvent on Ni-based catalysts prepared by solution combustion method for syngas methanation

Abstract Ni-Al2O3 catalysts prepared by solution combustion method for syngas methanation were enhanced by employing various heating rate and different solvent. The catalytic properties were tested in syngas methanation. The result indicates that both of heating rate and solvent remarkably affect Ni particle size, which is a key factor to the catalytic activity of Ni-Al2O3 catalysts for syngas methanation. Moreover, the relationship between Ni particle size and the production rate of methane per unit mass was correlated. The optimal Ni-Al2O3 catalyst prepared in ethanol at 2°C/min, achieves a maximum production rate of methane at the mean size of 20.8 nm.

Application of Response Surface Methodology and Central Composite Rotatable Design for Modeling and Optimization of Catalyst Compositions in Ethanol Synthesis via CO Hydrogenation

Abstract A statistical analysis about the effect of catalyst compositions on ethanol synthesis from CO hydrogenation was studied. The effect of Rh loading (0–3 wt.%), Fe loading (2–10 wt.%) and Mn loading (0.5–2.5 wt.%) of RhMnFe/γ-Al2O3 was studied through response surface methodology (RSM) combined with a central composite rotatable design (CCRD). A linear and a quadratic model were proposed to correlate the three variables to the two responses: CO conversion and ethanol selectivity. The predicted values for ethanol selectivity were in a good agreement with the experimental values, with R2 of 0.9779. The optimum conditions for achieving the maximum ethanol selectivity (27.8%) while limiting CO conversion at a moderate level (>20%) were as follows: Rh loading of 2.5 wt.%, Mn loading of 2.5 wt.% and Fe loading of 4 wt.%. Two representing catalysts were characterized by XRD, TPR and DRIFTS.

Hydrogen production via catalytic steam reforming of bio-oil model compound in a two-stage reaction system.

A mixture of several typical model compounds was chosen as the bio-oil model. Hydrogen production via catalytic steam reforming of model bio-oil in a two-stage reaction system was studied in this article. Quartz sand was used in the first-stage fluidized bed reactor for primary steam reforming, and Ni/modified dolomite was chosen as the catalyst in the second-stage fixed bed reactor for deep steam reforming. The main influential parameters, such as temperature, steam to carbon ratio, and weight hourly space velocity, were tested in this work. The optimum conditions on hydrogen production were obtained at 800°C; steam and carbon mole ratio, 12; and weight hourly space velocity, 1 h−1. In addition, there was a comparison between a two-stage reaction system and one-stage fixed bed reactor on the optimum condition. It was concluded that H2 yield decreased 5.6% in the two-stage reaction system and 9.9% in the one-stage fixed bed reactor after 3 h reaction time; the maximum carbon deposition ratio was 1 and 0.44%, gaseous carbon selectivity dropped from 93.6 and 90.1% to 83.4 and 78.4%. The fresh catalyst as well as used catalyst were analyzed by scanning electron microscopy, which showed that the carbon deposition in the two-stage reaction system is less than that of the one-stage fixed bed reactor.