Hydrolysis of cellobiose catalyzed by zeolites—the role of acidity and micropore structure

The roles of acidity and micropore structure of zeolite were studied in the hydrolysis of the model oligosaccharide of cellulose–cellobiose. HZSM-5, HY, HMOR and Hβ zeolites were selected as model catalysts for the hydrolysis of cellobiose. The effect of acidity of zeolite, including the strength, type and location, on its catalytic activity was investigated. The strong Br?nsted acid sites located in micropores are the active sites for the hydrolysis of cellobiose to glucose. Meanwhile, the catalytic performance of zeolite is also dependent on the micropore size of zeolite.     

The alcoholysis of acetonitrile prompted by Brфnsted acidic ionic liquid [HSO_3-pmim]HSO_4

Br(?)nsted acidic ionic liquids based on imidazolium cation were employed as a series of environmentally benign catalysts and mediums in the alcoholysis of acetonitrile to synthesize ester.The results showed that Br(?)nsted acidic ionic liquid [HSO_3- pmim]HSO_4 was an efficient catalyst and medium for the alcoholysis of acetonitrile which could be recycled easily without obvious decline in catalytic activity,the highest yield could reach 85%.     

The alcoholysis of acetonitrile prompted by BrФrnsted acidic ionic liquid [HSO3-pmim]HSO4

BrФnsted acidic ionic liquids based on imidazolium cation were employed as a series of environmentally benign catalysts and mediums in the alcoholysis of acetonitrile to synthesize ester. The results showed that BrФnsted acidic ionic liquid [HSO3- pmim]HSO4 was an efficient catalyst and medium for the alcoholysis of acetonitrile which could be recycled easily without obvious decline in catalytic activity, the highest yield could reach 85%.     

n-Dodecane Hydroconversion over Nickel Supported on Different Mesoporous Aluminosilicates

Introduction The hydroconversion of n-paraffins is achieved over bifunctional catalysts consisting of an acidic support and a hydrogenating/dehydrogenating metal compo-nent.1 During the reaction, the metal catalyses hydrogen transfer reactions, while isomerization and cracking oc-cur on the Br鰊sted acid sites.2,3 This reaction pathway determines that the proper ratio of metal/acid is impor-tant for the catalytic properties of the hydroconversion catalysts. The Pt, Pd or Ni promoted zeolite …     

六氢茚满催化开环: 氢解和阳离子反应路径(英文)

Perhydroindan(bicyclo[4.3.0]nonane) was converted in a flow-type apparatus under a hydrogen pressure of 5 MPa on six different catalysts,namely on a bifunctional Pd/Na,H-Beta zeolite,on Ir/Na,H-Y and Pt/Na,H-Y zeolites with a low concentration of Br?nsted acid sites,and on three catalysts containing the three noble metals on the non-acidic support silica.On the bifunctional zeolite Pd/Na,H-Beta,skeletal isomerization of perhydroindan was the primary reaction followed by opening of one naphthenic ring,the formation of open-chain nonanes in low yields of ca.6%,and hydrocracked products C8-.The carbon number distribution of the latter was volcano-shaped with no C1,C2,C7,and C8 indicating a carbocationic hydrocracking of C9 precursors with one naphthenic ring.On Ir/Na,H-Y and Pt/Na,H-Y("high-performance ring-opening catalysts"),ring opening and hydrocracking to C8-occurred by hydrogenolysis on the respective metal.Opening of the five-membered ring was found to be much faster than opening of the six-membered ring,in agreement with literature reports.The maximal selectivities of open-chain nonanes(OCNs) attained on Ir/Na,H-Y and Pt/Na,H-Y were very high,viz.49% and 54%,respectively,and significantly better than those of the open-chain decanes observed previously with decalin as model hydrocarbon.The OCNs formed on Pt/Na,H-Y were much less branched than those formed on Ir/Na,H-Y which was interpreted in terms of the different hydrogenolysis mechanisms on both metals.Valuable ancillary mechanistic information was obtained from the selectivities of perhydroindan hydroconversion on the three noble metals on silica.In contrast to Pd/silica,Ir/silica and Pt/silica gave appreciable selectivities of OCNs as well,yet the maximum values of these selectivities were lower than those obtained on the two high-performance zeolite catalysts.     

Effects of Calcination Temperature on the Acidity and Catalytic Performances of HZSM-5 Zeolite Catalysts for the Catalytic Cracking of n-Butane

The acidic modulations of a series of HZSM-5 catalysts were successfully made by calcination at different treatment temperatures, i.e. 500, 600, 650, 700 and 800 ℃, respectively. The results indicated that the total acid amounts, their density and the amount of B-type acid of HZSM-5 catalysts rapidly decreased, while the amounts of L-type acid had almost no change and thus the ratio of L/B was obviously enhanced with the increase of calcination temperature (excluding 800 ℃). The catalytic performances of modified HZSM-5 catalysts for the cracking of n-butane were also investigated. The main properties of these catalysts were characterized by means of XRD, N2 adsorption at low temperature, NH3-TPD, FTIR of pyridine adsorption and BET surface area measurements. The results showed that HZSM-5 zeolite pretreated at 800 ℃ had very low catalytic activity for n-butane cracking. In the calcination temperature range of 500-700 ℃, the total selectivity to olefins, propylene and butene were increased with the increase of calcination temperature, while, the selectivity for arene decreased with the calcination temperature.The HZSM-5 zeolite calcined at 700 ℃ produced light olefins with high yield, at the reaction temperature of 650 ℃ the yields of total olefins and ethylene were 52.8% and 29.4%, respectively. Besides, the more important role is that high calcination temperature treatment improved the duration stability of HZSM-5zeolites. The effect of calcination temperature on the physico-chemical properties and catalytic performance of HZSM-5 for cracking of n-butane was explored. It was found that the calcination temperature had large effects on the surface area, crystallinity and acid properties of HZSM-5 catalyst, which further affected the catalytic performance for n-butane cracking.     

BrФnsted Acidic Ionic Liquids as Efficient Catalysts and Mediums for the Synthesis of Half-esters: Structure-catalytic Selectivity Relationship

BrФnsted acidic ionic liquids based on imidazolium cation were employed as efficient catalysts and mediums for the ring opening of phthalic anhydride to synthesize half-esters. Good yields, short reaction time and mild reaction condition were achieved. Lower acidity of ionic liquid resulted in higher catalytic selectivity in the synthesis of half-esters. The minimum-energy geometries of sulfonic acid-functionalized ionic liquids based on imidazolium cation revealed that their acidities and catalytic selectivity in the synthesis of half-esters were related to their structures.     

Methane dehydro-aromatization over Mo/HZSM-5 catalysts in the absence of oxygen: Effect of steam-treatment on catalyst stability

The effect of steam-treatment to HZSM-5 zeolite and Mo/HZSM-5 with a steaming time range of 0.5-1 h on the catalytic performance of methane dehydro-aromatization (MDA) over Mo/HZSM-5 catalyst prepared with impregnation has been studied in detail in combination with the characterization of 1H MAS NMR technique. Both the deactivation rate constant (kd) and the Brnsted acid sites per unit cell were calculated to quantitatively evaluate the stability of Mo/HZSM-5 catalysts treated with steam at 813 K before and after impregnation of molybdenum species, and the corresponding variation of their Brnsted acid sites. The results reveal that a V-shape relationship between kd and the number of B1 acid sites per unit cell is presented on Mo/HZSM-5 catalyst under the tested steam-treatment and reaction conditions.     

Pd/Hβ-zeolite catalysts for catalytic combustion of toluene:Effect of SiO_2/Al_2O_3 ratio

The effect of pure and high silica Hβ zeolites on the catalytic performance of toluene combustion over Pd/Hβ catalyst was evaluated.Pure and high silica β zeolites were prepared by direct synthesis procedures,then 0.1 wt% of palladium was impregnated on different Hβ zeolites via in-cipient wetness technique using palladium nitrate as the Pd source.The Pd/Hβ catalysts were characterized by XRD,N2 adsorption/desorption,H2O adsorption,NH3-TPD,H2-TPR and XPS techniques.With increasing the SiO2/Al2O3 ratio of β zeolite,the activity of the Pd/Hβ catalysts for toluene combustion increased clearly and the pure silica β zeolite supported Pd catalyst showed the best catalytic activity.The superior catalytic performance of Pd/β catalyst prepared from pure silica β zeolite was attributed to its high hydrophobicity and the preserving ability for PdO active species.     

Pd/Hβ-zeolite catalysts for catalytic combustion of toluene: Effect of SiO2/Al2O3 ratio

The effect of pure and high silica Hβ zeolites on the catalytic performance of toluene combustion over Pd/H/3 catalyst was evaluated.Pure and high silica β zeolites were prepared by direct synthesis procedures,then 0.1 wt% of palladium was impregnated on different Hβ zeolites via incipient wetness technique using palladium nitrate as the Pd source.The Pd/Hβ catalysts were characterized by XRD,N2 adsorption/desorption,H2O adsorption,NH3-TPD,H2-TPR and XPS techniques.With increasing the SIO2/Al2O3 ratio of β zeolite,the activity of the Pd/Hβ catalysts for toluene combustion increased clearly and the pure silica β zeolite supported Pd catalyst showed the best catalytic activity.The superior catalytic performance of Pd/β catalyst prepared from pure silica β zeolite was attributed to its high hydrophobicity and the preserving ability for PdO active species.     

Effects of P content in a P/HZSM-5 catalyst on the conversion of ethanol to hydrocarbons

A series of P/HZSM-5 catalysts prepared by impregnation method were used for ethanol conversion to lower olefins. The catalysts were characterized by X-ray diffraction (XRD), NH3-temperature-programmed desorption (NH3-TPD) and N2 adsorption-desorption measurements. It was found that the P/HZSM-5 catalysts showed high activity and selectivity toward light olefins. The selectivities of propylene and butylene can be improved with the introduction of phosphorus (P). When the content of P reached 3.0 wt%, more than 18.9% propylene in the gaseous products was obtained over the P/HZSM-5 catalyst at 450 ?C. The introduction of P modified the strong Br?nsted acid sites of the original HZSM-5 catalysts and P/HZSM-5 catalysts could resist coke formation and showed good stability.     

Promotional effect of cerium on nickel-containing mesoporous silica for carbon dioxide reforming of methane

A series of Ce-promoted 6.7%Ni-containing mesoporous silica(Ce-Ni-Si O2)with varying Ce content(0.5%–4.8%)was prepared using the evaporation-induced self-assembly method.The characterization results showed that Ce and Ni species were homogeneously incorporated into the mesoporous silica matrix.The catalytic properties of these samples in the dry reforming of methane reaction revealed that the catalysts(e.g.,1.2%Ce-Ni-Si O2)containing highly dispersed small Ni particles exhibited excellent catalytic activity and long-term stability,which is attributed to the anchoring effect of the Ce and its ability to increase surface oxygen species concentration.     

The effect of FER zeolite acid sites in methanol-to-dimethyl-ether catalytic dehydration

In this paper, the effect of acidity of zeolites with FER framework was studied in the methanol dehydration to dimethyl ether reaction, by comparing catalysts with different Si/Al ratios(namely 8, 30 and60). The aim of this work was to investigate how the acid sites concentration, strength, distribution and typology(Br?nsted and Lewis) affect methanol conversion, DME selectivity and coke formation. It was found that the aluminium content affects slightly acid sites strength whilst a relevant effect on acid sites concentration and distribution(Br?nsted/Lewis) was observed as 24% of Lewis sites were found on Alrichest samples, whilst less than 10% of Lewis acid sites were observed on FER at higher Si/Al ratio. All the investigated catalyst samples showed a selectivity toward DME always greater than 0.9 and samples with the lowest Si/Al ratio exhibit the best performances in terms of methanol conversion, approaching the theoretical equilibrium value(around 0.85) at temperatures below 200 °C. Turnover-frequency analysis suggests that this result seems to be related not only to the higher amount of acid sites but also that the presence of Lewis acid sites may play a significant role in converting methanol. On the other hand, the presence of Lewis acid sites, combined with a high acidity, promote the formation of by-products(mainly methane) and coke deposition during the reaction. As final evidence, all the investigated catalysts exhibit very high resistance to deactivation by coke deposition, over 60 h continuous test, and a GC–MS analysis of the coke deposited on the catalyst surface reveals tetra-methyl benzene as main component.     

Comparison of the activities of binder-added and binder-free Mo/HZSM-5 catalysts in methane dehydroaromatization at 1073 K in periodic CH4-H2 switch operation mode

Three industry-supplied,well-shaped Mo/HZSM-5 catalysts,two binder-added and one binder-free,were tested for the first time in methane dehydroaromatization to benzene at 1073 K and 10000 mL/(g h)in periodic CH4-H2 switch operation mode,and their catalytic performances were compared with those of three self-prepared,binder-free powder Mo/HZSM-5 catalysts.XRD,27Al NMR,SEM,BET and NH3-TPD characterizations of all the catalysts show that the zeolites in the two binder-added catalysts are comparable to those in the three binder-free powder catalysts in crystallinity,crystal size,micropore volume and Brnsted acidity.The test results,on the other hand,show that the catalytic performances of the two binder-added catalysts are worse than those of the four binder-free catalysts on both catalyst mass and zeolite mass bases.Then,TPO and BET measurements of all spent samples were conducted to get a deep insight into the negative effects of binder addition, and the results suggest that the binder additives functioned mainly to enhance the polyaromatization of formed aromatics to coke on their external surfaces and consequently lower the benzene formation activity and selectivity of the catalyst.     

Catalytic Synthesis of Hexyl-naphthalene over H-type Zeolites

H-type zeolites（ HY, Hβ, and HM） were synthesized and characterized by XRD, NH3-TPD, and Py-IR. Selectively catalytic alkylation of naphthalene with n-hexanol to hexyl-naphthalene over the zeolites was carried out. The experimental results show that the catalytic activities of the zeolites are mainly determined by their acid properties and pore structures. The larger the pore diameter is, the higher the catalytic activity is. NH3-TPD profiles show that Hβ and HM have lower acid strengths than HY. HY has both the highest activity and highest selectivity for the hexylnaphthalene. Higher reaction temperatures and longer reaction time are beneficial to the production of β-hexyl-naphthalene over the HY zeolite.     

Catalytic Combustion of Methane over High Copper-Loading ZSM-5 Catalysts

Two series of Cu/ZSM-5 catalysts,loading from 5 to 20 wt% CuO,were prepared by the deposition-precipitation and impregnation methods,respectively.The catalysts prepared by the impreg- nation method showed better catalytic performances than those prepared by the deposition-precipitation method and the increase of copper loading favored methane conversion.20Cu(I)/ZSM-5 had the highest activity with T_(90%)of 746 K,and for 20Cu(D)/ZSM-5,T_(90%)was as high as 804 K.The characteriza- tion of X-ray diffraction(XRD),temperature-programmed reduction(TPR),temperature-programmed desorption(TPD),and X-ray photoelectron spectroscopy(XPS)revealed that the dispersion of cop- per species could be improved by using the deposition-precipitation method instead of the impregnation method,but the fraction of surface CuO,corresponding to active sites for methane oxidation,was larger on 20Cu(I)/ZSM-5 than 20Cu(D)/ZSM-5.The results of Pyridine-Fourier transform infrared spectrum (Py-FT-IR)showed that a majority of Lewis acidity and a minority of Brφnsted acidity were present on Cu/ZSM-5 catalysts.20Cu(I)/ZSM-5 presented more Lewis acid sites.The number of Lewis acid sites changed significantly with preadsorption of oxygen.Adsorption of methane and oxygen on acid sites was observed.The properties of Cu/ZSM-5 catalysts were correlated with the activity for methane oxidation.     

CO oxidation over Co_3O_4/SiO_2 catalysts:Effects of porous structure of silica and catalyst calcination temperature

The catalytic performances of Co3O4/SiO2 catalysts prepared by incipient wetness impregnation for CO oxidation were investigated using three kinds of silica as carriers with different pore sizes of 7.7,14.0 and 27.0 nm.The effects of calcination temperature on the catalyst surface and micro structure properties as well as catalytic performance for the oxidation of carbon monoxide were also studied.All catalysts were characterized by N2 adsorption-desorption,XRD,XPS,FTIR,H2-TPR and O2-TPD.It was found that the properties and crystal size of cobalt-containing species strongly depended on the pore size of silica carrier.While the silica pore size increased from 7.7 to 27.0 nm,the Co3O4 crystal size increased from 8.5 to 13.5 nm.Moreover,it was demonstrated that if the spinel crystal structure of Co3O4 was obtained at a calcination temperature as low as 150℃,the catalyst sample would have a high Co3O4 surface dispersion and an increase of surface active species,and thus exhibit a high activity for the oxidation of carbon monoxide.     

Effects of Citric Acid Concentration and Activation Temperature on the Synthesis of Carbon Nanotubes

A series of Ni-La-Mg catalyst samples were prepared by citric acid complex method, and carbonnanotubes were synthesized by catalytic decomposition of CH4 on these catalysts. The effects of the citricacid concentration and the activation temperature on catalytic activity were investigated by CO adsorption,TEM and XRD techniques. The experimental results showed that the particle size of the catalysts preparedthrough gel auto-combustion varied with the concentration of citric acid. Therefore carbon nanotubes with different diameters were obtained correspondingly. The effect of activation temperature on the activity of catalyst was negligible from 500 to 700℃, but it became pronounced at lower or higher temperatures.     

Characterization and Activity of Cr, Cu and Ga Modified ZSM—5 for Direct Conversion of Methane to Liquid Hydrocarbons

Direct conversion of methane using a metal-loaded ZSM-5 zeolite prepared via acidic ion exchange was investigated to elucidate the roles of metal and acidity in the formation of liquid hydrocarbons. ZSM-5 (SiO2/A12O3=30) was loaded with different metals (Cr, Cu and Ga) according to the acidic ion-exchange method to produce metal-loaded ZSM-5 zeolite catalysts. XRD, NMR, FT-IR and N2 adsorption analyses indicated that Cr and Ga species managed to occupy the alllmlnum positions in the ZSM-5 framework. In addition, Cr species were deposited in the pores of the structure. However, Cu oxides were deposited on the surface and in the mesopores of the ZSM-5 zeolite. An acidity study using TPD-NH3, FT-IR, and IR-pyridine analyses revealed that the total number of acid sites and the strengths of the BrSusted and Lewis acid sites were significantly different after the acidic ion exchange treatment.Cu loaded HZSM-5 is a potential catalyst for direct conversion of methane to liquid hydrocarbons. The successful production of gasoline via the direct conversion of methane depends on the amount of aluminum in the zeolite framework and the strength of the BrSnsted acid sites.