Youming Ni

Preparation of hierarchical mesoporous Zn/HZSM-5 catalyst and its application in MTG reaction

Abstract The hierarchical mesoporous Zn/ZSM-5 zeolite catalyst was prepared by NaOH treatment and Zn impregnation, and its application in the conversion of methanol to gasoline (MTG) was studied. N2 adsorption-desorption results showed that the mesopores with sizes of 2-20 nm in HZ5/0.3AT was formed by 0.3 M NaOH alkali treatment. The zeolite samples after modification were also characterized by XRF, AAS, XRD, SEM and NH3-TPD methods. Zn impregnated catalyst Zn/HZ5/0.3AT exhibited dramatic improvements in catalytic lifetime and liquid hydrocarbons yield. The selectivity of aromatic hydrocarbons was also improved after Zn impregnation. It is suggested that the mesopores of Zn/HZ5/0.3AT enhanced the synergetic effect of Zn species and acid sites and the capability to coke tolerance, which were confirmed by the results of catalytic test and TGA analysis, respectively.

Facile synthesis of hierarchical nanocrystalline ZSM-5 zeolite under mild conditions and its catalytic performance

Hierarchical nanocrystalline ZSM-5 zeolite (NZ5) was synthesized at 100 °C under atmospheric pressure using methylamine as a mineralizing agent. The crystallization process of NZ5 was characterized by dynamic light scattering (DLS), X-ray diffraction (XRD), and infrared spectroscopy (FTIR). The results of contrastive experiments showed that evaporation of the solvent promoted the aggregation of primary particles, and the addition of methylamine accelerated the crystallization process. The NZ5 aggregate consisted of 20 nm individual particles, as shown in scanning electron microscope (SEM). The lattice fringes in the transmission electron microscope (TEM) images and the XRD results indicated that individual particles of NZ5 were highly crystalline. N(2) adsorption-desorption isotherms showed that NZ5 had high BET surface areas with mesopores having a mean diameter of about 9 nm. NZ5 exhibited a long lifetime, a stable and high yield of liquid hydrocarbons, and a high anti-coking performance in methanol-to-hydrocarbons reaction. Catalytic testing and TGA results showed that the lifetime of NZ5 was about ten times longer than that of micro-sized ZSM-5 zeolite (MZ5), and the average coking rate with NZ5 was one fifth over that of MZ5.

Promotion effect of Fe in mordenite zeolite on carbonylation of dimethyl ether to methyl acetate

A series of Fe-modified mordenite zeolite samples were synthesized by a template-free method and employed in dimethyl ether (DME) carbonylation reaction for the production of methyl acetate (MAc). XRD, UV-Vis, and UV-Raman characterization studies proved that Fe atoms have been introduced into the mordenite zeolite framework by partial substitution of Al atoms, which led to evident changes of activity and MAc selectivity. With the increase of iron content (as metal) from 0.0 to 3.6 wt%, DME conversion first increased and then decreased. MAc selectivity and catalyst stability were enhanced for all Fe-modified samples. TG and GC-MS analysis of deactivated catalysts showed that the amount of coke retained in the catalysts decreased as the iron content of the zeolites increased. The enhancement effects were expounded in terms of the decrease of the acid strength and acid density in the 12MR channels of mordenite after introduction of Fe, resulting in the reduction of carbon deposition.

Phosphorous-modified ordered mesoporous carbon for catalytic dehydrogenation of propane to propylene

Phosphorous (P)-modified ordered mesoporous carbon CMK-3 was used as a catalyst for the direct dehydrogenation (DH) of propane to propylene without any auxiliary stream, and this catalyst exhibited better activity and selectivity than the pristine ordered mesoporous carbon. The prepared samples were characterized by N2 adsorption and desorption, temperature-programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS). After the introduction of P using an impregnation method, PO groups formed on the surface of the materials and substantially improved the activity and selectivity. The PO groups are believed to be electron donors for CO active centers, or independent active centers for catalytic DH of propane.

The effect of ethanol on the performance of CrOx/SiO2 catalysts during propane dehydrogenation

Abstract The effects of ethanol vapor pretreatment on the performance of CrO x /SiO 2 catalysts during the dehydrogenation of propane to propylene were studied with and without the presence of CO 2 . The catalyst pretreated with ethanol vapor exhibited better catalytic activity than the pristine CrO x /SiO 2 , generating 41.4% propane conversion and 84.8% propylene selectivity. The various catalyst samples prepared were characterized by X-ray diffraction, transmission electron microscopy, temperature-programmed reduction, X-ray photoelectron spectroscopy and reflectance UV-Vis spectroscopy. The data show that coordinative Cr 3+ species represent the active sites during the dehydrogenation of propane and that these species serve as precursors for the generation of Cr 3+ . Cr 3+ is reduced during the reaction, leading to a decrease in catalytic activity. Following ethanol vapor pretreatment, the reduced CrO x in the catalyst is readily re-oxidized to Cr 6+ by CO 2 . The pretreated catalyst thus exhibits high activity during the propane dehydrogenation reaction by maintaining the active Cr 3+ states.

A highly efficient Nafion-H catalyst for vapour phase carbonylation of dimethoxymethane

A highly active Nafion-H catalyst is developed for vapour phase carbonylation of dimethoxymethane (DMM) to methyl methoxyacetate (MMAc) with a significant MMAc selectivity as high as 90%. The excellently catalytic performance is because of the unique structure and high acid strength of the Nafion-H catalyst.

A green route for methanol carbonylation

Acetic acid is one of the most important bulk commodity chemicals and is currently manufactured by methanol carbonylation reactions with rhodium or iridium organometallic complexes and halide-containing promoters named Monsanto or BP Cativa™ homogeneous processes, respectively. Developing a halide-free catalyst and a heterogeneous process for methanol carbonylation is of great importance and has recently attracted extensive research attention. Here, we report a green route for direct synthesis of acetic acid via vapor-phase carbonylation of methanol with a stable, selective, halide-free, and noble metal-free catalyst based on pyridine-modified H-mordenite zeolite. Methanol conversion and acetic acid selectivity can reach up to 100% and 95%, respectively. Only little deactivation is observed during the 145 hour reaction.

Coupling of Methanol and Carbon Monoxide over H-ZSM-5 to Form Aromatics

The conversion of methanol into aromatics over unmodified H-ZSM-5 zeolite is generally not high because the hydrogen transfer reaction results in alkane formation. Now circa 80 % aromatics selectivity for the coupling reaction of methanol and carbon monoxide over H-ZSM-5 is reported. Carbonyl compounds and methyl-2-cyclopenten-1-ones (MCPOs), which were detected in the products and catalysts, respectively, are considered as intermediates. The latter species can be synthesized from the former species and olefins. C isotope tracing and C liquid-state NMR results confirmed that the carbon atoms of CO molecules were incorporated into MCPOs and aromatic rings. A new aromatization mechanism that involves the formation of the above intermediates and cooccurs with a dramatically decreased hydrogen transfer reaction is proposed. A portion of the carbons in CO molecules are incorporated into aromatic, which is of great significance for industrial applications. Aromatics, especially benzene, toluene, and xylene (BTX), are important bulk chemicals that are primarily produced from petroleum by catalytic reforming or cracking. Obtaining aromatics from non-petroleum resources, such as coal, natural gas, or biomass, is very important because of the increase in market demand for such products and the depletion of petroleum resources. Methanol can be derived from these alternative resources via syngas chemistry, and aromatics can be readily synthesized from methanol by a methanol-to-aromatics (MTA) reaction. Generally, acidic ZSM-5 zeolites are selected as MTA catalysts owing to their unique topology and three-dimensional micropore systems. However, acidic H-form ZSM-5 zeolite (H-ZSM-5) without metal modifications usually has low aromatics selectivity because of the corresponding formation of alkanes via hydrogen transfer. Although modifications with metals such as Zn, Ga, and Ag increase aromatics formation by enhancing the dehydrogenation of alkanes via catalysis by these metal species, some methanol decomposition and the formation of unrecoverable catalyst structure owing to metal evaporation, segregation, and aggregation are inevitable. 5] Recently, Cheng et al. reported that aromatization could be enhanced by CO over the bifunctional ZnZrOx/H-ZSM-5 catalysts in the conversion of syngas or intermediate methanol because CO plays a role in the removal of H species and subsequent formation of methanol. As a result, it can be deduced that ZnZrOx is indispensable to the catalysis mechanism. In the presence of CO, H-zeolites catalyze methanol carbonylation to form methyl acetate (MeOAc) and acetic acid (HOAc) through the Koch reaction. It has been proposed that the formation of the first carbon–carbon bond occurs through methanol carbonylation during the methanol to olefin reaction. Herein we report an aromatics selectivity of 80% along with 65 % BTX for the coupling reaction of methanol and CO (CMTA) over H-ZSM-5 zeolite. A new aromatization mechanism in which the hydrogen transfer reaction is sharply decreased is proposed. The CMTA and MTA reactions were performed at 673 K under 4.0 MPa over Z-25 (H-ZSM-5 with the SiO2/Al2O3 ratio = 25). The results are shown in Figure 1a, an approximate 40% initial aromatics selectivity with a 53% C2–C4 paraffin selectivity was obtained under N2, which agree with the typical hydrogen transfer mechanism. Interestingly, the initial aromatics selectivity was dramatically increased to 80% along with 65 % BTX when methanol was coupled with CO, while the CH4 and C2–C4 paraffin selectivity was only 3% and 20 %, respectively (Figure 1b). The detailed selectivity of aromatics is shown in the Supporting Information, Figure S1. As presented in the Supporting Information, Figure S2, increasing the reaction temperatures of the CMTA reaction was advantageous to aromatics generation because C2–C4 paraffin formation was suppressed; however a much higher temperature (723 K) led to lower aromatics selectivity owing to sharp increases in CH4. H-ZSM-5 zeolites with SiO2/Al2O3 ratios ranging from 25 to 175 were employed to study the effect of acidity on aromatization in the CMTA reaction. The XRD, N2 absorption–desorption, and NH3-TPD results are depicted in the Supporting Information, Figure S3, Table S1, and Figure S4, respectively. A lower SiO2/Al2O3 ratio results in more acidic sites. As seen in Figure 2, the aromatics selectivity increased [*] Z. Chen, Dr. Y. Ni, Dr. Y. Zhi, F. Wen, Z. Zhou, Prof. Dr. Y. Wei, Prof. Dr. W. Zhu, Prof. Dr. Z. Liu National Engineering Laboratory for Methanol to Olefins Dalian National Laboratory for Clean Energy Dalian Institute of Chemical Physics Chinese Academy of Sciences, Dalian 116023 (P. R. China) E-mail: wlzhu@dicp.ac.cn