The reaction of isobutane over Ni/SiO2 catalyst changes from hydrogenolysis to dehydrogenation when Sn is introduced. The adsorption modes and energies of isobutane and isobutene over the Ni/SiO2 catalyst with and without Sn addition were determined by in situ FTIR and a novel transient response adsorption approach. In the absence of Sn, isobutane is adsorbed in a double-site mode with H atoms in two methyl groups of isobutane, facilitating hydrogenolysis of isobutane. After the addition of Sn, a single-site adsorption mode with the H atom in the methylidyne group is speculated instead, which is beneficial to the rupture of the C–H bond rather than the C–C bond. Moreover, the double-site adsorption mode of isobutene with the C═C bond and the H atom in a methyl group is turned into single-site mode with the C═C bond after the introduction of Sn. As for the adsorption energy of isobutene, the introduction of Sn leads to an obvious decrease from 74 to 50 kJ mol–1 and facilitates the prompt desorption of isobutene, resulting in a high selectivity of 81.9 wt %.Keywords: adsorption energy; adsorption mode; hydrogenolysis; isobutane dehydrogenation; Ni/SiO2 catalyst; Sn addition;

Effects of operating conditions on residue fluid catalytic cracking (RFCC) were studied in a pilot-scale FCC unit. Experimental results indicated that both high reaction severity and long residence time promoted the production of ethylene and propylene. A novel RFCC process for maximum ethylene and propylene (MEP) production was further proposed, which was characterized by high operating severity, application of olefin-selective catalyst, and stratified reprocessing of light gasoline and butenes. Simulation experiments of the MEP process demonstrated that both light cycle gasoline and recycled butenes were effectively converted; meanwhile, the semispent catalyst still retained sufficient activity to further crack residue feedstock. When treating Daqing AR, the MEP process yielded up to 8.85 wt % ethylene and 25.97 wt % propylene. In contrast, due to elevated catalyst activity in a second-stage riser, the two-stage riser MEP process produced more propylene and LPG at the expense of light oil. Also, ethylene yield was still up to a comparative level.

Selective hydrogenation and subsequent catalytic cracking of light cycle oil (LCO) from a fluid catalytic cracking unit is expected to produce more high-octane-number gasoline. In this process, the multi-ring aromatics are selectively hydrogenated and transformed to naphthenic aromatics, which are further converted into the gasoline fraction through cracking reaction. This work has systematically studied the effect of catalyst composition on the cracking performance of hydrogenated LCO (hydro-LCO). The results indicate that, the cracking activity of LCO was substantially improved after hydrogenation. In comparison to the ZSM-5-zeolite-based catalyst, both an efficient conversion of hydro-LCO to gasoline and a greatly enhanced hydrogen transfer reaction were obtained over the Y-zeolite-based catalyst, further resulting in a higher hydrogen utilization efficiency. In addition, the active acid sites for hydro-LCO cracking were inferred, and a possible reaction network was proposed.

•Weakly-acidic silicalite-1 zeolite is active in catalyzing toluene methylation.•The silanol nests inside zeolite micropores are determined to be the active sites.•The inert external surface is responsible for the enhanced selectivity to p-xylene.•The reaction network of toluene methylation over silicalite-1 zeolite is concluded.In this study, a series of MFI-type zeolites with different aluminum contents have been prepared and evaluated for toluene alkylation with methanol. All these zeolite samples are well crystallized and exhibit typical characteristics of MFI structure (as indicated by XRD), and their acid amounts decrease continuously with the decreasing aluminum content of the zeolites (as revealed by NH3-TPD). The weakly-acidic aluminum-free silicalite-1 zeolite is demonstrated to be active in catalyzing toluene methylation for the first time. The content of p-xylene in xylenes, namely the reaction para-selectivity, has been substantially improved by increasing the zeolite diffusion resistance. For the silicalite-1 zeolite, the silanol nests inside the micropores are determined to be the active sites for toluene methylation into p-xylene. Meanwhile, the external surface enriching inert isolated silanols is indicated to be responsible for the enhanced para-selectivity, due to a negligible isomerization of as-formed p-xylene into its isomers. Generally, a greatly improved catalytic performance (with a para-selectivity up to 75% and p-xylene yield ca. 13%) has been obtained for silicalite-1 among the recently reported zeolites.Download high-res image (120KB)Download full-size image

•Incomplete removal of coke leads to a decrease in overall activity without the reduction in the isobutane formation rate.•Peaks in NH3-TPD profiles at 500-700 °C are caused by a redox reaction between strongly adsorbed NH3 and superacid sites.•Incomplete removal of coke and appropriate decrease in the density of SO42− selectively promoted monomolecular pathway.The relationship between the heterogeneity of active sites and isomerization mechanism of n-butane over alumina-promoted sulfated zirconia (SZA) was elucidated by two series of catalysts with different surface properties. The incomplete removal of coke deposition leads to a decrease in overall activity without the reduction of the rate of isobutane formation. Subjecting the fresh SZA catalyst to the thermal treatment at 650 °C causes a striking decrease in activity, resulting from the decrease in the superacidity and oxidizability of the catalyst. While the thermal treatment at 600 °C only selectively suppresses the side reactions. It is found that the peaks in NH3-TPD profiles at 500–700 °C are caused by a redox reaction between strongly adsorbed ammonia and superacid sites by in situ NH3-TPD-MS measurements. Thus, this peak reflects the strength of superacidity and oxidizability. At the beginning of the reaction, the effective oxidative and protonative activation routes result in the higher concentration of intermediates, which facilitates the “dimerization-isomerization-cracking” reactions. The incomplete removal of coke and the appropriate decrease in the density of sulfate species on the surface selectively promoted the monomolecular pathway.Download high-res image (92KB)Download full-size image

A series of Ce-La/MgAl2O4-x catalysts were prepared by the incipient wetness impregnation method and characterized by BET, XRD, H2-TPR, CO-TPR and in situ FT-IR. The results demonstrate that the catalyst with a Mg/Al molar ratio of 0.5 yields the most uniform dispersion of CeO2 and greatly enhances formation of Ce-O-La solid solution, resulting in the increase of oxygen vacancy and surface Ce3+ content. Thereby, the synergistic effect between surface Ce3+ and oxygen vacancy gives rise to the best catalytic performance of NO reduction. Moreover, introduction of Mg species suppresses tranformation of CeO2 to Ce(SO4)2/Ce2(SO4)3 and then improves the SO2 resistance performance of Ce-La/MgAl2O4−0.5.

In this work, physical mixtures of ZnO and Ga2O3, even with a small amount of Ga2O3, were found to exhibit greatly enhanced catalytic performance for isobutane dehydrogenation compared to their individual components, namely solely ZnO or Ga2O3. The activity test results under different packing patterns indicated that, the interface between the two component oxides played a crucial role in improving the dehydrogenation performance. Moreover, consistent with the highest dehydrogenation reactivity, the largest activation energy for isobutane desorption over ZnO–Ga2O3 was determined using an isobutane-TPD test. The observed synergistic effect of ZnO and Ga2O3 could be understood as being that, Lewis acid sites provided by Ga2O3 promoted the heterolytic cleavage of C–H bonds in isobutane over ZnO, thereby increasing the isobutane conversion. On the surface of ZnO–Ga2O3, a double-site adsorption of isobutane was further speculated through FT-IR spectra analysis, and one-step decomposition was probably the actual reaction pathway of isobutane. In addition, from understanding that catalyst deactivation was caused by highly graphitized coke deposition, the deactivated catalyst was regenerated through air combustion, and good catalyst stability was demonstrated through continuous reaction–regeneration cycles.

High gas-solid contact efficiency and low solid back-mixing are necessary to both promote methanol conversion and inhibit side reactions. Thus, a novel multi-regime reactor with dense-phase reaction section and dilute-phase conveying region was designed. The reactor promoted stable reaction activity during a 300 h pilot-scale evaluation with high yields of propylene and gasoline. A process for maximum propylene and gasoline production from methanol (PGFM) characterized by moderate operating severity, application of ZSM-11 catalyst and novel reactor, and stratified reprocessing or etherification of light gasoline and C4 olefins was proposed. The PGFM process can be implemented in the existing FCC process and is considered to be more economic and flexible.

The promoting effect of sulfate species in propane dehydrogenation over Fe2O3/γ-Al2O3 catalysts is systematically elucidated by using iron(III) or iron(II) sulfate as the precursor, pre-treating with SO2 or introducing SO2 with propane as the reactant. At 560 °C, up to 23 wt% propylene yield with 80% selectivity is obtained. It is demonstrated that the introduced sulfate species exist in the form of SO42− and strongly interact with the support and Fe via the Al–O–S bond and the Fe–O–S bond. On one hand, it suppresses the formation of FexC species and thus the cracking reaction. On the other hand, it leads to an enhanced adsorption capacity of propane. Meanwhile, the initial C–H bond activation and subsequent rupture with the formation of Fe–C3H7 and OH are facilitated, resulting in excellent dehydrogenation performance. Online MS, XPS, XRD and reaction–regeneration–sulfuration results show that the loss of sulfate species by the reduction to S2− and release in the form of SO2 is the main reason for the deactivation of the sulfated catalysts.

Viewpoints on the influence of matrix acidity on the catalytic cracking of heavy oil are still inconsistent, hindering the studies of the reaction routes that occur during the matrix-precracking process. In this study, the effects of matrix acidity on heavy oil cracking were systematically studied by preparing alumina and modified alumina with different acidity in a practically meaningful range as the matrix components of fluid catalytic cracking catalysts. Results showed that Brönsted sites presented a much higher activity than Lewis sites on the matrix surface. Increasing the Brönsted acid strength of matrices improved the activity of catalysts, with the aggravated product distribution, while increasing the Lewis acid strength of matrices aggravated the product distribution and decreased the catalyst activity. Interestingly, results also showed that contacting Lewis sites first followed by interacting with Brönsted sites during the matrix-precracking process would facilitate heavy oil cracking more deeply. In addition, a new reaction route was proposed that protolytic cracking route should occur during the matrix-precracking process when cracking heavy oil. Based on this result, one can modify the matrix of the catalyst by introducing Brönsted sites or not to achieve high yield of light olefin or maximize liquid products.

•Fast-turbulent fluidized bed (FTFB) riser with expanding section and ring-feeder was investigated.•Two types of ring-feeder (mixed and vortex) were used to improve gas–solid contact efficiency.•Two probability peaks of solid fraction signals existed in FTFB riser with vortex ring-feeder.•Ring-feeder structure affected flow dynamics and gas–solid contact efficiency in FTFB risers.The flow dynamics in a novel fast-turbulent fluidized bed (FTFB) with middle-upper expanding structure and two different ring-feeder internals (mixed and vortex ring-feeder) were studied to achieve a reduction in gasoline olefin production. Compared with a conventional circulating fluidized bed, the novel FTFB displayed unique characteristics and advantages. A higher solids holdup and more uniform solids holdup distribution existed in the diameter-expanding region, especially for the FTFB with vortex ring-feeder structure. A probability density distribution analysis indicated that the novel fluidized bed could reduce gas–solids segregation and enhance gas–solids interaction. A constant carbon dioxide tracer system was used to simulate the reactant gas distribution. The gas–solids contact efficiency was defined according to the solid dispersibility and the amount of gas covering the solid surface. Novel FTFB risers, especially those with vortex ring-feeders, have a much higher gas–solids contact efficiency than that of traditional risers.

HZSM-5-based catalyst is a recognized catalyst which is particularly selective towards the formations of aromatics in the methanol reaction. However, studies on HZSM-5-based catalyst were mainly focused on the addition of metallic or/and nonmetallic element. Quite few studies have reported the effect of active matrix such as γ-alumina on the aromatization of methanol. In this study, γ-alumina was introduced into HZSM-5-based catalyst for the purpose of investigating the effect of γ-alumina in methanol to aromatics reaction. The catalysts were characterized by X-ray diffraction, Temperature-programmed Desorption of NH3 (NH3-TPD), Pyridine adsorption FT-IR diffuse reflection spectroscopy and adsorption–desorption measurements of nitrogen, respectively. Characterizations showed that the introduction of γ-alumina increased the amount of mesopores and acid sites in the catalyst. The experimental mainly includes two parts. Firstly, separate reaction performances over the catalyst with/without γ-alumina and γ-alumina showed that γ-alumina could significantly promote the formations of aromatics. However, γ-alumina alone could merely convert methanol to dimethyl ether with a minor quantity of gaseous hydrocarbons. Acid properties showed that the introduction of γ-alumina increased the percentage of Lewis acid on catalyst surface and enhanced acid strength, as a result, promoted the production of active intermediates which was essential for aromatic formation. The rise of aromatics selectivity might be caused by the combined effect of acid site density and acid strength. Follow-up work was mainly focused on the effect of the loading amount and loading order of the catalyst with γ-alumina. Results indicated that the total aromatic yield increased gradually with the increasing amount of catalyst with γ-alumina regardless of the loading order of the catalyst with γ-alumina. Gasoline compositions showed that the increased aromatics were at the expense of paraffins, olefins, and naphthenes. Besides, all single aromatic hydrocarbons increased gradually with the increasing amount of catalyst with γ-alumina. And the aromatics had a larger variation change when methanol first passed through the catalyst with γ-alumina.

H-ZSM-5-based catalyst is a recognized catalyst which is particularly selective towards the formations of light olefins in the methanol reaction. A series of H-ZSM-5 (SiO2/Al2O3 = 38) modified with different amounts of magnesium have been investigated. All the samples were characterized by X-ray diffraction instrument (XRD), temperature-programmed desorption of NH3 (NH3-TPD) and Fourier Transform Infrared Spectoscopy (FT-IR). The results indicated that the impregnation of H-ZSM-5 (SiO2/Al2O3 = 38) zeolite with various magnesium loading amount significantly affected the strength of acid sites and decreased the concentration of both weak and strong acid sites. As a result of modification, magnesium mainly interacted with strong Brønsted acid sites, thus generated new medium strong acid sites and enhanced the yield of propylene. The optimum acid property for methanol to propylene (MTP) reaction was gotten over 4.0 Mg-ZSM-5 (4.0 wt% Mg) zeolite catalyst. The maximum yield of propylene was 10.62 wt% over 4.0 Mg-ZSM-5 zeolite catalyst by the 30 min on stream. Coke which was mostly formed on strong Brønsted acid sites, would cause the catalysts deactivation, so the reduction of strong Brønsted acid sites could enhance the catalytic stability.

Metal sulfide catalysts were highly efficient in the activation of C–H bond for isobutane dehydrogenation, and the dehydrogenation performance was better than that of the commercial catalysts Cr2O3/Al2O3 and Pt–Sn/Al2O3, providing a class of environmentally friendly and economical alternative catalysts for industrial application.Keywords: dehydrogenation; isobutane; isobutene; metal sulfide; sulfidation

In this work, to optimize the catalytic performance of Co-based catalysts for isobutane dehydrogenation, the effects of support, calcination temperature and some promoters were investigated systematically. Results of activity tests and catalyst characterization jointly indicated that both the support and calcination temperature influenced Co dispersion, catalyst acid properties and the interaction between support and Co species significantly. Consequently, the adsorption–desorption behaviors for isobutane and isobutene as well as the dehydrogenation performance were further affected. Sulfided Co/SiO2, with no acidity, exhibited the best performance. Although high calcination temperature was beneficial for achieving a high selectivity to isobutene over Al2O3 and MgAl2O4 supported Co-based catalysts, the inevitable formation of Co2SiO4 over Co/SiO2 at high temperature led to reduced active sites and dehydrogenation activity. In addition, by comparing the different effects of the separate introduction of S, Sn, Cu and Cl, it was concluded that an efficient promoter should present the following characteristics: inhibition of the formation of metal ensembles, and strong binding affinity to two hydrogen atoms of one additive atom.

Ni/HZSM-5 catalysts with γ-alumina were prepared by the sol–gel method. At first, reaction performances were investigated over the HZSM-5 catalysts with and without γ-alumina. Then, reaction evaluations were conducted over the Ni/HZSM (different loading amounts of nickel species were investigated) catalysts with and without γ-alumina. The addition of nickel species and γ-alumina increased the total acidity of the catalysts. Furthermore, the introduction of γ-alumina increased the amount of mesopores in the catalysts. Nickel species were much more stable with the presence of γ-alumina. Both nickel species and γ-alumina contributed the aromatization of methanol.

Ni/MgAl2O4 catalysts with high NiO loadings were highly active for isobutane cracking, which led to abundant formation of methane, hydrogen and coke. The results of activity testing and XRD characterization jointly revealed that large ensembles of metallic nickel species formed during reaction notably catalyzed cracking instead of dehydrogenation. However, after introduction of sulfur into Ni/MgAl2O4 catalyst through impregnation with ammonium sulfate, undesired cracking reactions were effectively inhibited, and the selectivity to isobutene increased remarkably. Totally, up to ∼42 wt % isobutene could be obtained at 560 °C in a single pass after the modification. From the characterization results, it was also concluded that, after sulfur introduction, NiO particles became much smaller and better dispersed on the catalyst surface. NiS species, formed during the induction period of the reaction, not only facilitated isobutene desorption from the catalyst, but also constituted the active sites for isobutane dehydrogenation. In addition, due to the appearance of NiS species, Ni/MgAl2O4 catalyst after H2S/H2 sulfuration exhibited a high initial activity without experiencing an induction period, further confirming the crucial role that introduced sulfur played.Keywords: dehydrogenation; isobutane; Ni/MgAl2O4 catalysts; NiS; sulfur addition

The most critical problem of processing coker gas oil (CGO) is its high nitrogen content, especially the basic nitrogen compounds, which limits its cracking performance in the fluid catalytic cracking (FCC) process. For enhancing the conversion of CGO, three processing schemes were evaluated in a pilot-scale riser FCC unit. Four indexes (thermal cracking index, dehydrogenation index, hydrogen transfer coefficient, and isomerization reaction index) were used to investigate the effects of operating conditions on the reactions of CGO cracking. Results show that the optimal operating conditions for CGO cracking are high reaction temperature and large catalyst-to-oil ratio with a short residence time. Therefore, we proposed a synergistic process by selectively recycling light FCC gasoline (LCG) from the upper position of the riser reactor, which can provide a high-severity reaction zone for CGO cracking and a low-severity reaction zone for gasoline upgrading. To further investigate the mutual effect of the two feeds, different recycle ratios of LCG were tested. Results indicate that the conversion of CGO significantly increased with the LCG recycle ratio. When the recycle ratio reached 50 wt %, the gasoline could be upgraded at a higher efficiency. To ensure the optimal recycle ratio and improve the gasoline quality, a two-stage synergistic (TSS) process was proposed. The simulated experiments of the TSS process show that the higher conversion and more desired products can be achieved, even though under a high processing ratio of CGO to conventional feeds.

In this article, an environmentally friendly non-noble-metal class of Mo/MgAl2O4 catalysts is demonstrated to exhibit excellent performance in isobutane dehydrogenation. Results of activity tests indicated that an induction period is required for the catalysts to develop the active species. Further investigation revealed that high-valence-state Mo species are favorable for the initial oxidative reactions and Mo4+ ions are probably the actual active species for catalytic dehydrogenation. Given the strongly endothermic characteristics and rapid catalyst deactivation of alkane dehydrogenation, a circulating fluidized-bed unit was further applied to evaluate the activity and stability of the catalysts. To avoid undesired oxidative reactions and improve the initial catalytic activity, a flow of hydrogen was introduced into the pilot-scale unit to prereduce the catalysts prior to reaction. In general, the catalysts exhibited highly active and stable performance in the pilot-scale evaluation, with an isobutene yield of up to 35 wt %, demonstrating great potential for industrial applications.

•C-TFB was identified as DSU regime on the macro operating level.•Maximum solid holdup migration happened under high-density conditions.•Worst gas–solid contact efficiency model was constructed.•Novel parameter describing contact efficiency was brought up.•C-TFB improves flow dynamics and gas–solid contact efficiency.Circulating-turbulent fluidized bed (C-TFB) was characterized by high solid holdup, homogenous axial and radial flow structure, no net downflow of solids and high contact efficiency in this study. These flow dynamic properties were mainly represented by solid holdup profiles, the identification of flow regime and cluster dynamics in a riser, 100–150 mm in diameter and 10.06 m in height. To quantify the effect of novel diameter-expanding structure on flow dynamics, a parameter (contact efficiency) was introduced firstly. The effects of gas–solid interaction on flow performance were investigated by a fiber-optic probe to detect solid holdup. CO2 tracer injection and sampling system were used to characterize the flow structure and define the contact efficiency. The experimental results showed that flow regime in C-TFB is belonging to dense riser upflow (DRU) or dense-suspension upflow (DSU) regimes and transient region disappears in axial position. Flow structure is different from previous studies about traditional circulation fluidized bed (CFB) due to the effect of expanding structure and ring-feeder internal. A flow model based on the profiles of solid holdup and CO2 tracer concentration was proposed to account for the gas–solid contact efficiency in the reactor. The contact efficiency in C-TFB is much higher than that of high-density circulating fluidized bed (HDCFB), which means C-TFB reactor would exhibit better performance to optimize the product distribution under the same operating conditions.

The continuous deterioration of feedstocks, the increasing demand of diesel, and the increasingly strict environmental regulations on gasoline call for the development of fluid catalytic cracking (FCC) technology. To increase the feed conversion and the diesel yield as well as produce low-olefin gasoline, the multifunctional two-stage riser (MFT) FCC process was proposed. Experiments were carried out in a pilot-scale riser FCC apparatus. Results show that a higher reaction temperature is appropriate for heavy cycle oil (HCO) conversion, and the semispent catalyst can also be used to upgrade light FCC gasoline (LCG). The synergistic process of cracking HCO and upgrading LCG in the second-stage riser can significantly enhance the conversion of HCO while reducing the olefin content of gasoline at less expense of gasoline yield. Furthermore, the novel structure riser reactor can increase the conversion of olefins in gasoline. Because of the significant increase of HCO conversion, the fresh feedstock can be cracked under mild conditions for producing more diesel without negative effects on the feed conversion. Compared with the TSR FCC process, in the MFT FCC process, the increased feed conversion, diesel and light oil yields can be achieved, at the same time, the olefin content of gasoline decreased by approximately 17 wt %.

A core/shell structure composite was synthesized via a new method of pre-coating one raw material. The composite was characterized by X-ray diffraction, SEM, TEM and N2 isothermal adsorption–desorption and Py-FTIR. In addition, the catalytic performance of the composite in cracking of heavy oil for producing olefin was also investigated. The characterization results show that the composite with a core/shell structure had smaller particle size, uniform SAPO-5 shell, and fewer acid sites than ZSM-5, accelerating the transport of reactant and product molecules between different zeolites. Consequently, the light olefins on the composites had high specific selectivity.

The regeneration mechanism of sulfur species formed on the Mg-Al-Ce-Fe mixed-spinel sulfur-transfer additives is clarified in this paper. Sulfate is the main sulfur species on the sulfur-transfer catalysts after the oxidative adsorption of SO2, and the S–O bond within sulfates shows lower stability in spinel phase than in the MgO phase. The reduction of these sulfate species leads to the emission of SO2 as well as H2S, and the formation of the two reductive products are both correlated with the change in Mg/Al ratio; however, SO2 is much more sensitive. When the regeneration was conducted at 550 °C, only H2S was observed as a reductive product; yet, at 700 °C, the small amount of H2S was preceded by a large amount of SO2. The mechanism for the sulfate reductive decomposition has been proposed that sulfite is the intermediate, which can be pyrolyzed into SO2 or undergo redox reaction to form H2S. The pyrolysis reaction is closely related to the relative magnitudes of the energy provided and required to break the S–O bond in sulfates, while the probability of the redox reaction is more likely to be dependent on the H2 concentration. Sulfur-transfer additives with more surface-active sites should be developed to enhance the reductive ability, since more time is needed for the bulk-like sulfate to be reduced.

A series of the Mn/MgAl mixed oxides were prepared by using acid-processed gelatin method, characterized by XRD, TEM and BET techniques, and applied as sulfur transfer catalysts. It is found that the mixed oxides catalysts achieve the highest oxidative rate when they contain 10% PEG1000. The results also show that the catalytic oxidative rate increases with the surface area of the catalyst.

Oligomerization of ethylene in fluidized catalytic cracking (FCC) dry gas was investigated as a feasible route for the use of FCC dry gas. A series of metal-loaded HZSM-5 (MZSM-5) catalysts were prepared by the impregnation method. It was characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and N2 adsorption that the metal introduction did not change the structure of the HZSM-5 catalyst but had an influence on acidic properties, i.e., decreasing Brönsted acid sites and forming Lewis acid sites together with the blocking of channels. The catalytic performances of MZSM-5 catalysts for the oligmerization of ethylene in FCC dry gas were studied in a fixed-bed reactor. It was observed that the addition of metal to fresh HZSM-5 enhanced the olefin yield. Among all catalysts studied, MgZSM-5 exhibited the highest propylene and total olefin yields of 12.21 and 17.28%, respectively. Higher olefin yields were obtained over the steam-treated HZSM-5 catalyst when adding moderate N2 as a diluent gas. The catalytic performance of the steam-treated HZSM-5 catalyst was also investigated in a fluidized-bed reactor, and similar product distribution could be obtained in comparison to that in a fixed-bed reactor. The conversion of ethylene could reach 47.22% at 500 °C with a propylene yield of 14.32%.

ZSM-5 zeolites and magnesium−aluminate spinels have been widely used as fluid catalytic cracking (FCC) additives to improve propene yield and reduce SO2 emission, respectively. In this study, these two components were combined into a single particle to obtain novel bifunctional additives. Meanwhile, a commercial propene additive (ZSM-5/kaolin), in which the Si/Al ratio of ZSM-5 was the same as that of bifunctional additives, was used as a reference. The effects of adding the bifunctional additives containing MgAl2O4 and the commercial propene additive ZSM-5/kaolin to the base catalyst in cracking of vacuum gas oil (VGO) were investigated. Results showed that the bifunctional additive with unmodified ZSM-5 was less active in increasing the propene yield. However, modifying ZSM-5 with both La and P could enhance the performance of the bifunctional additive, resulting in boosts in LPG and propene yields, which can be compared to those in the case of ZSM-5/kaolin. Also, the performances of the SO2 oxidative adsorption over the additives were examined. It showed that both bifunctional additives presented higher uptake capability of SO2 than ZSM-5/kaolin. The samples were characterized by X-ray diffraction (XRD), N2 adsorption−desorption techniques, X-ray fluorescence (XRF), 31P and 27Al magic angle spinning (MAS) nuclear magnetic resonance (NMR), and Fourier transform infrared (FTIR) spectra of adsorbed pyridine methods. Results indicated that the Mg2+ ion exchanged with hydroxyl groups of zeolite during the incorporation of MgAl2O4 impaired the zeolite framework during steaming, which can be significantly weakened by modifying ZSM-5 with both La and P.

AbstractOne type of ZSM-5 zeolite with large partical size was prepared and characterized by XRD, SEM, N2 adsorption-desorption, XRF, Py-IR and NH3-TPD techniques. Effects of ammonium exchange and SiO2/Al2O3 molar ratios on the reaction of methanol to propylene (MTP) over Na-ZSM-5 and H-ZSM-5 zeolites have been studied in a fixed-bed flow reactor under the operating conditions of T = 500 °C, P = 1 atm, and WHSV = 6 h−1. Ammonium exchange led to a rapid decrease in Na content for Na-ZSM-5 zeolite. The reaction results indicated that Na-ZSM-5 and H-ZSM-5 with different SiO2/Al2O3 molar ratios all exhibited high activity for methanol conversion. Ammonium exchange and the decreased SiO2/Al2O3 molar ratio of ZSM-5 zeolite led to an increase both in strong acid sites and weak acid sites. Na-ZSM-5 with high SiO2/Al2O3 molar ratio was favorable for the formation of propylene. The highest propylene selectivity (45.9%) was obtained over Na-ZSM-5 zeolite catalyst with SiO2/Al2O3 molar ratio of 220.

AbstractA series of manganese-promoted MgAlFe mixed oxides, used as sulfur transfer catalysts, were prepared by acid-processed gelatin method and characterized by TGA-DTA, XRD, N2 adsorption-desorption and FT-IR techniques. It was found that the sulfur transfer catalysts with 0.5–3.0 wt% manganese showed its good dispersion in the precursor. The novel Mn/MgAlFe catalysts with 0.5–5.0 wt% manganese oxide showed a high oxidative adsorption rate and sulfur adsorption capacity, and 5.0 wt% Mn/MgAlFe sample was superior to the others for SO2 removal. Moreover, the presence of CO had no obvious effect on the adsorption activity of sulfur transfer catalysts for SO2 uptake.

The oligomerization of ethylene in FCC dry gas over HZSM-5 catalyst with different Si/Al2 ratios was studied. The effect of acid density of catalyst on the oligomerization of ethylene was discussed. By increasing the acid density of catalyst, ethylene conversion showed a linear increase, while the yields of olefins decreased when the acid density of catalyst exceeded 0.14 mmolNH3/g owing to a promotion of hydrogen transfer reaction. Through comparing the average distance between acid sites on catalyst with kinetic diameters of olefins, it was found that the dimerization of ethylene was not restrained by the sparse distribution of acid sites, while the hydrogen transfer reaction of C3 and C4 olefins was limited. On these bases, a conclusion is proposed that the dimerization of ethylene proceeded via Eley-Rideal mechanism, while the hydrogen transfer reaction of C3 and C4 olefins followed the Langmuir-Hinshelwood mechanism.

The matrix catalytic function when cracking the feed oil with large molecular size was systematically studied using three different catalyst configurations, including staged bed, partly mixed bed and completely mixed bed. Results showed that molecules in the feed oil with large molecular size indeed preferred to be first precracked on the matrix surface and then entered into the zeolite pores during the practical reaction process. Furthermore, the matrix catalytic function exhibited a great matrix-precracking ability to large feed molecules, which considerably increased the catalyst activity and the light oil selectivity. Besides the much better accessibility, the matrix-precracking ability was also from the similar capability to crack large feed hydrocarbons into the moderate fragments with that of the zeolite component. More interestingly, the interactions between the matrix catalytic function and the zeolite catalytic function made the catalyst not only exhibit much more catalytic advantages of the zeolite component, but also retain the matrix-precracking ability. As a result, the interactions enhanced the catalyst activity and improved the product distribution at the same time. The matrix catalytic function is indispensable for the catalytic cracking of feed with large molecular size, although the matrix component itself presented an inferior catalytic performance than the zeolite component did.The matrix catalytic function is indispensable for the catalytic cracking of feed with large molecular size, although the matrix component itself presented an inferior performance than the zeolite component did.Download high-res image (140KB)Download full-size image

In order to develop the conversion of heavy oil with a high yield of propylene in the catalytic cracking process, ZSM-5 zeolite was modified by tungsten and phosphorus, which was proved to be an effective method. Characterization results show that the improvement of catalytic performance could be correlated to the interaction of phosphorus and tungsten species on ZSM-5. P inhibited the aggregation of tungsten species on ZSM-5 and was conductive to convert the tungsten species with octahedral coordination into tetrahedral coordination. And this ultimately led to that more acid sites were reserved after hydrothermal treatment in the tungsten and phosphorus co-modified ZSM-5 catalyst. Phosphorus species played an important role to restrain the dehydrogenation activity of tungsten. In addition, a model reflecting the interaction between tungsten species and ZSM-5 framework was proposed.Tungsten and phosphorus on ZSM-5 exhibited a synergistic effect on improving the performance of ZSM-5 catalyst for maximizing the propylene in FCC process.Download full-size image

•Polymeric Si–O–Sn2+ are active species rather than metallic Sn.•Deactivation of SnO2/SiO2 is related to reduction of active species rather than the coke formation.•Addition of Ni improves the stability of SnO2/SiO2 but diminishes its activity.Different with Wang et. al.’s study, we found that polymeric Si–O–Sn2+ rather than Ni-Sn alloy and metallic Sn are active species in silica-supported tin oxide catalysts for dehydrogenation of propane. The results showed that high surface area of mesoporous silica brought about high dispersion of tin oxide species, as a result, catalytic activity and stability were both improved. DRUV–vis, XPS, TPR and XRD studies of fresh and reduced catalysts indicated that the deactivation was related to the reduction of active species rather than the coke formation since active tin species cannot maintain its oxidation state at reaction conditions (high temperature and reducing atmosphere). The formed Ni3Sn2 alloy after reduction just functioned as promoter which accelerated the desorption of H2 and regeneration of active site. A synergy effect between active tin species and Ni3Sn2 alloy were observed.

The promoting effect of sulfate species in propane dehydrogenation over Fe2O3/γ-Al2O3 catalysts is systematically elucidated by using iron(III) or iron(II) sulfate as the precursor, pre-treating with SO2 or introducing SO2 with propane as the reactant. At 560 °C, up to 23 wt% propylene yield with 80% selectivity is obtained. It is demonstrated that the introduced sulfate species exist in the form of SO42− and strongly interact with the support and Fe via the Al–O–S bond and the Fe–O–S bond. On one hand, it suppresses the formation of FexC species and thus the cracking reaction. On the other hand, it leads to an enhanced adsorption capacity of propane. Meanwhile, the initial C–H bond activation and subsequent rupture with the formation of Fe–C3H7 and OH are facilitated, resulting in excellent dehydrogenation performance. Online MS, XPS, XRD and reaction–regeneration–sulfuration results show that the loss of sulfate species by the reduction to S2− and release in the form of SO2 is the main reason for the deactivation of the sulfated catalysts.

In this work, physical mixtures of ZnO and Ga2O3, even with a small amount of Ga2O3, were found to exhibit greatly enhanced catalytic performance for isobutane dehydrogenation compared to their individual components, namely solely ZnO or Ga2O3. The activity test results under different packing patterns indicated that, the interface between the two component oxides played a crucial role in improving the dehydrogenation performance. Moreover, consistent with the highest dehydrogenation reactivity, the largest activation energy for isobutane desorption over ZnO–Ga2O3 was determined using an isobutane-TPD test. The observed synergistic effect of ZnO and Ga2O3 could be understood as being that, Lewis acid sites provided by Ga2O3 promoted the heterolytic cleavage of C–H bonds in isobutane over ZnO, thereby increasing the isobutane conversion. On the surface of ZnO–Ga2O3, a double-site adsorption of isobutane was further speculated through FT-IR spectra analysis, and one-step decomposition was probably the actual reaction pathway of isobutane. In addition, from understanding that catalyst deactivation was caused by highly graphitized coke deposition, the deactivated catalyst was regenerated through air combustion, and good catalyst stability was demonstrated through continuous reaction–regeneration cycles.