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1.
Hydrothermal conversion of rice husk ash to faujasite-types and NaA-type of zeolites 总被引:1,自引:0,他引:1
The faujasite-type of zeolites (NaX and NaY) and NaA-type of zeolite were synthesized from rice husk ash (RHA) via the hydrothermal
conditions. The combustion of rice husk at controlled temperature of 600 °C for an hour in open air produce more than 90%
of amorphous silica in the ash which was reactive towards the synthesis of zeolites. The formation of zeolite NaY from RHA
is metastable and thus, the seeding and ageing effects in the synthesis of zeolite NaY were investigated to avoid the formation
of zeolite A or P as the impurities in zeolite NaY. Zeolites NaX and NaA were also successfully synthesized with high purity,
absence of impurities and other phases, and high reproducibility. Thus, the amorphous forms of silica in RHA can be used as
a source of silica for the synthesis of faujasite-types and NaA-type of zeolites. 相似文献
2.
The synthesis of hydrocarbons from catalytic hydrogenation of CO/H2 was investigated over Co/zeolite catalysts at 1 atm, 493–553 K, H2/CO = 2, and GHSV = 1200. Various zeolites, such as NaA, NaX, NaY, KL and NaMordenite, were used as the supports. The catalysts were prepared by impregnation and were characterized by H2/CO chemisorption and temperature-programmed reduction (TPR). Based on TPD measurements, the CO/H2 adsorption ratio can be used as an index for the extent of metal-zeolite interaction. The stronger the metal-zeolite interaction is, the higher the Co/H2 adsorption ratio on metal is. The activity and selectivity of cobalt supported in zeolites were affected by complex factors such as framework structure, Si/Al ratio, and the complementary cations. The activity of the catalyst is in the order: Co/KL > Co/NaX > Co/NaY > Co/NaMordenite > Co/NaA. All of the Co/zeolite catalysts had a very high selectivity to C2–C4 olefins, which would decrease with increasing reaction temperature. Cobalt oxide supported in zeolite was difficult to reduce. Increasing the reduction temperature could increase the reducibility of cobalt and resulted in the increase of activity. 相似文献
3.
Chlorination of toluene with sulfuryl chloride was studied using NaX and NaY zeolites as catalysts under conditions where ring chlorination predominates. The zeolites are more selective than conventional Lewis acid catalysts with initial para-chlorotoluene : ortho-chlorotoluene ratios of 1.2. Both faujasites studied underwent rapid deactivation under reaction conditions. The deactivation of NaX was much more rapid than that of NaY. The accumulation of polychlorinated toluenes in the pores of the catalyst may be initially responsible for the loss of activity. In the case of NaY, this lost activity can be partially recovered by soaking the catalyst in fresh toluene, whereas attempts to regenerate by burning out the deposited materials cause a rapid disintegration of the catalyst. Zeolite fouling is accompanied by a more severe dealumination process that eventually leads to structural collapse and complete loss of activity. 相似文献
4.
Sung Dae Yim Kwang-Hyun Chang Dong Jun Koh In-Sik Nam Young Gul Kim 《Catalysis Today》2000,63(2-4):215-222
The oxidation of perchloroethylene (PCE) was investigated over chromium oxide catalysts supported on SiO2, SiO2–Al2O3, activated carbon, mordenite type zeolites, MgO, TiO2 and Al2O3. Supported chromium oxide catalysts were more active than any other metal oxide catalysts including noble metal examined in the present study. PCE removal activity of chromium oxide catalysts mainly depended on the type of supports and the content of metal loaded on the catalyst surface. TiO2 and Al2O3 containing high surface areas were effective for the high performance of PCE removal, since the formation of well dispersed Cr(VI) active reaction sites for the present reaction system, was enhanced even for the high Cr loading on the catalyst surface. CrOx catalysts supported on TiO2 and Al2O3 also exhibited stable PCE removal activity at a low feed concentration of PCE of 30 ppm up to 100 h at 350°C. However, significant catalyst deactivation was observed at high PCE concentration of 10 000 ppm. CrOx/TiO2 revealed stronger water tolerance than CrOx/Al2O3 due to the surface hydrophobicity. 相似文献
5.
The CoCr2O4 and CrOx/γ-Al2O3 catalysts were used for the oxidative decomposition of trichloroethylene (TCE). Both catalysts showed an initial deactivation at low temperatures around 280 °C, mainly due to the dissociative adsorption of reactant TCE. This was confirmed by the temperature programmed oxidation of TCE where the carbon oxides were formed up to a temperature below 300 °C. Possible changes in the oxidation state of chromium species were observed with XANES and ESR. During the oxidation reaction at low temperatures, the Cr(VI) species were reduced to Cr(III) species, which seemed to be coupled with TCE adsorption. At higher temperatures, however, the Cr(VI) species appeared again and the catalytic activity was completely recovered. 相似文献
6.
Fluidizable catalysts are developed in this study for advancing an integral approach towards a new methane reforming process. With this end, catalysts constituted by nickel supported on -alumina, NaY, and USY were developed using the incipient wetness technique producing bulk nickel loadings in the 0–20 wt.% range. These catalysts were also tested under relevant conditions for industrial operation in a novel Riser Simulator. It was found that, for the case of ‘dry’ reforming of methane, nickel deposited in zeolites is a promising catalyst given that it allows for close control of metal dispersion–redispersion process. In fact, when this catalyst was exposed to repeated oxidation and reduction cycles, nickel dispersions remained stable at 25% for NaY zeolite and at 15% for USY zeolite. This catalyst offers, however, limited application for steam reforming of methane given the potential collapse of the zeolite structure under steam atmosphere. As an alternative and for cases where steam reforming of methane is preferred, nickel on -alumina catalyst was considered. In these cases, optimum catalytic activity was achieved with 2.5 wt.% of nickel on -alumina with 3–6% nickel dispersion. 相似文献
7.
Isosteric Heat of Adsorption of n-Ethane on Zeolites NaX and NaY Using a volumetric method isotherms of adsorption of ethane on zeolites NaX and NaY were measured. The Clausius-Clapeyron equation was used to calculate the isosteric heat of adsorption of the paraffin on both molecular-sieves. These enthalpies show a linear dependence of the amount of adsorbed molecules. The zeolite with the higher charge density shows a larger heat of adsorption. The difference in the heat of adsorption is explained by adsorption on different centers in the cavity of both zeolites. 相似文献
8.
Cristian Covarrubias Rafael García Jorge Yánez Renán Arriagada 《Journal of Porous Materials》2008,15(4):491-498
The preparation of organomodified zeolites with different framework structures (FAU, LTA and MOR) using N-cetylpyridinium bromide (CPB) as tailoring agent was studied. The sorption properties of CPB-modified zeolites were evaluated
in the removal of tannery contaminants from aqueous solution. The CPB-modified FAU-type zeolite presented the highest Cr(VI)
retention capacity (37 mmol/kg) due to the higher Cr(VI) retention of its unmodified form (larger pore opening) and its high
CPB sorption capacity. CPB-modified FAU zeolite also exhibited high thermal stability as consequence of special interactions
between the CPB molecules and the zeolite surface. In addition, the intrinsic Cr(III) exchange capacity of FAU zeolite increased
with CPB loading (162–527 mmol/kg), which appear to be due to an additional retention mechanism provided by the sorbed cetylpyridinium
surfactant layer. On other hand, CPB-modified FAU zeolite also exhibited high toluene retention capacity (62 mmol/kg) due
to of the hydrophobic character of its surfactant-modified surface and toluene adsorption on internal sorption sites of FAU
zeolite. Thus, CPB-modified FAU zeolite appears as a promising adsorbent for simultaneous removal of Cr(III), Cr(VI) and toluene
contaminants from aqueous solution. 相似文献
9.
Evaluation of H-type zeolites in the destructive oxidation of chlorinated volatile organic compounds 总被引:3,自引:0,他引:3
J. R. Gonzlez-Velasco R. Lpez-Fonseca A. Aranzabal J. I. Gutirrez-Ortiz P. Steltenpohl 《Applied catalysis. B, Environmental》2000,24(3-4):233-242
The deep oxidation of 1,2-dichloroethane (DCE) and trichloroethylene (TCE) over H-type zeolites (H-Y and H-ZSM-5) was evaluated. Experiments were performed at conditions of lean hydrocarbon concentration (around 1000 ppmv) in dry air, between 200 and 550°C in a conventional fixed-bed reactor. H-ZSM-5 zeolite resulted more active than H-Y zeolite in the decomposition of both chlorinated volatile organic compounds. It was established that Brønsted acidity plays an important role in controlling the catalytic behaviour of the H-type zeolites. DCE was completely decomposed at 400°C, whereas TCE required higher temperatures (550°C). Vinyl chloride was identified as an intermediate in the DCE oxidation in the range of 250–400°C. When vinyl chloride is destroyed at higher temperatures, both zeolite catalysts show a high selectivity (>90%) towards HCl formation. Trace amounts of tetrachloroethylene were detected in the TCE oxidation, which peaked at 500°C. CO was promoted in quantity in the destruction of both DCE and TCE reflecting the difficulty of carbon monoxide oxidation over H-type zeolites. 相似文献
10.
The catalytic oxidation of isopropanol and o-xylene alone and in mixture was investigated over basic zeolites (CsX and NaX) and an acidic zeolite (HY). For a given temperature, the conversion of VOCs mixture into CO2 increases with the basicity of the zeolite. Results show that VOCs are oxidized through a basic mechanism over NaX, and through an acidic mechanism over HY. Over HY, the presence of isopropanol increases the oxidation of o-xylene, probably because of the formation of isopropyldimethylbenzenes obtained via an acidic mechanism. The addition of platinum over zeolites increases the rate of the VOCs oxidation, this behavior being more pronounced over PtHY maybe because of a higher Pt dispersion. 相似文献
11.
Copper-ceria catalysts for CO oxidation supported on 4A, 5A, NaX and NaY zeolites were prepared by incipient wetness impregnation and excess-solution impregnation. Catalysts were characterized by SEM, EDX, XRD, N2 adsorption-desorption, H2-TPR and XPS. Results revealed that the catalysts were greatly affected by zeolites and preparation method. EDX results indicated the metal loading of 4A-ES (5.1 wt% Cu, 15.7 wt% Ce), 5A-ES (5.9 wt% Cu, 19.2% Ce), NaX-ES (11.7wt% Cu, 4.2 wt% Ce) and NaY-ES (11.0 wt% Cu, 7.9 wt% Ce) greatly varied. TPR results suggested that the peak at around 195 °C was presented in NaX-ES and 4A-IW, standing for dispersed copper species that is very active for CO oxidation. The catalytic activity of 4A-ES and NaX-ES was the best among catalysts made by excess-solution impregnation, demonstrated by the lowest T50 at 127 and 129 °C, respectively. The catalytic activity of catalysts made by incipient wetness impregnation was worse than that of catalysts made by excess-solution impregnation, examined by the T50 of 4A-IW and NaX-IW at 128 and 192 °C, respectively. 相似文献
12.
13.
Jan-Jezreel F. Saceda Kamolwan Rintramee Supattra Khabuanchalad Sanchai Prayoonpokarach Rizalinda L. de Leon Jatuporn Wittayakun 《Journal of Industrial and Engineering Chemistry》2012,18(1):420-424
Zeolite Y in sodium form (NaY) was synthesized using silica source from rice husk, transformed to ammonium form (NH4Y), and calcined to convert to proton form (HY). The direct conversion of NH4Y to HY resulted in loss of the zeolite crystallinity and lower surface area. Thus, the NH4Y was further used in the preparation of cerium (Ce) catalysts. The NH4Y was also treated with a basic solution in an attempt to generate mesopores but only site defects were likely formed. The supported Ce catalysts with good Ce dispersion were prepared by wetness impregnation of Ce precursor solution on NaY, NH4Y, and base-treated NH4Y. Upon calcination, the generated catalysts were notated as Ce/NaY, Ce/HY, and Ce/YB. In catalytic testing on ethanol oxidation at varying temperature in a continuous laboratory-scale fixed-bed reactor, all the zeolites gave low ethanol conversion at 100–300 °C. The catalytic activity significantly improved with the presence of Ce. The Ce/YB showed the higher ethanol conversion and CO2 yield than Ce/NaY and Ce/HY probably because of the presence of more local site defects on the zeolite. 相似文献
14.
Zahra Ghasemi Iman Sourinejad Hossein Kazemian Mojtaba Hadavifar Sohrab Rohani Habibollah Younesi 《Chemical Engineering Communications》2020,207(6):808-825
AbstractThe Na-P1 zeolite was produced from coal fly ash and modified with different environmental friendly surfactants. The potential of these green modified zeolites was investigated as adsorbents for Cr(VI) ions in a batch system. XRD, SEM, XRF, and ICP-AES analyses were used for the characterization of raw materials and zeolite samples. The environmental friendly modified zeolites successfully immobilized different toxic elements in their framework inhibiting the transfer of these toxic elements to the surrounding liquid phase. The effects of various operational parameters on Cr(VI) removal were studied. The Hexamethylenediamine (HDTMA) and Ammonyx KP (KP) modified zeolites had larger chromium removal potential than the other samples at all temperatures. The effectiveness of Cr(VI) ions elimination became greater as the pH decreased and the adsorbent dose increased. The Freundlich, Langmuir, and Dubinin–Radushkevich isotherms were fitted to the equilibrium data. The Dubinin–Radushkevich and Langmuir models gave a better fitness to equilibrium data of HDTMA-Na-P1 and KP-Na-P1, respectively. The positive and high ΔH° values showed the endothermic nature of the total Cr(VI) sorption procedure and indicated that Cr(VI) adsorption onto HDTMA-Na-P1 and KP-Na-P1 is a chemisorption. The negative ΔS° values also showed that chromium ions were stable on the surface of adsorbents. The adsorption potential of the developed eco-friendly KP-Na-P1 was higher than those of other adsorbents reported in the literature. 相似文献
15.
Eva Díaz Salvador Ordez Aurelio Vega Jos Coca 《Applied catalysis. B, Environmental》2005,56(4):313-322
Hexane deep oxidation was studied over NaX and CaA zeolites modified by ion exchange with transition metals (Mn2+, Co2+, Fe3+), the percentage of ion exchanged, determined by ICP-MS, varying between 39 and 98%. Parent and exchanged zeolites were characterized by X-ray diffraction (XRD), N2 physisorption, temperature-programmed reduction (TPR), oxygen and ammonia temperature-programmed desorption (TPD) and inverse gas chromatography (IGC). Catalytic activities were evaluated through the recording of light-off curves in a pulsed microreactor, catalytic activity being correlated with physicochemical properties of the solids (crystallinity, surface acidity, adsorption properties and morphological parameters). As general trend, CaA zeolites are more active than NaX zeolites. Mn-exchanged CaA zeolite was the most active catalyst for hexane oxidation, whereas the addition of Fe to the zeolites leads to strong chemical and morphological changes in the parent zeolite. 相似文献
16.
Influence of the exchanged cation in Pd/BEA and Pd/FAU zeolites for catalytic oxidation of VOCs 总被引:1,自引:0,他引:1
H.L. Tidahy S. Siffert J.-F. Lamonier R. Cousin E.A. Zhilinskaya A. Aboukaïs B.-L. Su X. Canet G. De Weireld M. Frre J.-M. Giraudon G. Leclercq 《Applied catalysis. B, Environmental》2007,70(1-4):377-383
0.5 wt% palladium supported on exchanged BEA and FAU zeolites were prepared, characterized and tested in the total oxidation of volatile organic compounds (VOCs). The BEA and FAU zeolites were exchanged with different cations to study the influence of alkali metal cations (Na+, Cs+) and H+ in Pd-based catalysts on propene and toluene total oxidation. The exchange with different cations (Na+, Cs+) and H+ led to a decrease of the surface area and the micropore volume. All Pd/BEA and Pd/FAU zeolites were found to be powerful catalysts for the total oxidation of VOCs. They were active at low temperature and totally selective for CO2 and H2O. However, their activity depends significantly on the type of zeolite and on the nature of the charge-compensating cation. The activity order for propene and toluene oxidation on FAU catalysts, Pd/CsFAU > Pd/NaFAU > Pd/HFAU, is the reverse of the activity order on BEA catalysts: Pd/HBEA > Pd/NaBEA > Pd/CsBEA. The catalytic activities can be rationalized in terms of the influence of the electronegativity of the charge-compensating cation on the Pd particles, the Pd dispersion, the PdO reducibility and the adsorption energies for VOCs. 相似文献
17.
Olivier Villain Georges Calas Laurence Gaioisy Laurent Cormier Jean-Louis Hazemann 《Journal of the American Ceramic Society》2007,90(11):3578-3581
The oxidation state of chromium in glasses melted in an air atmosphere with and without refining agents was investigated by Cr K-edge X-ray absorption near-edge structure (XANES) and optical absorption spectroscopy. A good agreement in the relative proportion of Cr(III) and Cr(VI) is obtained between both methods. We show that the chemical dependence of the absorption coefficient of Cr(III) is less important in XANES than in optical absorption spectroscopy. The comparison of optical absorption and XANES spectra of glasses melted under different conditions provides an indirect assessment of the molar extinction coefficient of Cr(VI) in glasses. 相似文献
18.
Some Ru and Co carbonyl clusters in zeolite pores such as Ru3(CO)12/NaY, [HRu6(CO)18]–/NaY, [Ru6(CO)18]2–/NaX, Co4(CO)12/NaY and Co6(CO)16/NaY were prepared by the ship-in-bottle technique, and characterized by FTIR and EXAFS. The RuCo bimetallic carbonyl cluster was prepared by reductive carbonylation of the oxidized RuCo/NaY, which provides the proposed assignment to [HRUCo3(CO)12]/NaY. The tailored Ru, RuCo and Co catalysts were prepared by H2 reduction from the precursors, e.g. Ru, RuCo bimetallic and Co carbonyl clusters impregnated on SiO2 and entrapped in NaY and NaX zeolites. The RuCo bimetallic carbonyl cluster-derived catalysts showed substantially higher activities and selectivities for oxygenates such as C1–C5 alcohols in CO hydrogenation (CO/H2 = 0.33-1.0, 5 bar, 519–543 K). By contrast, hydrocarbons such as methane were preferentially obtained on the catalysts prepared from Ru6, Ru3 and Co4 carbonyl clusters and provided lower CO conversion and poor selectivities for oxygenates. The RuCo bimetals are proposed to be associated with the selective formation of higher alcohols in CO hydrogenation. 相似文献
19.
Performance of zeolites and product selectivity in the gas-phase oxidation of 1,2-dichloroethane 总被引:1,自引:0,他引:1
R. Lpez-Fonseca A. Aranzabal P. Steltenpohl J. I. Gutirrez-Ortiz J. R. Gonzlez-Velasco 《Catalysis Today》2000,62(4):367-377
The deep oxidation of 1,2-dichloroethane (DCE) over H-type zeolites (H-Y, H-ZSM-5 and H-MOR) was evaluated. Experiments were performed on conditions of lean chlorocarbon concentration (around 1000 ppmv) under dry and humid conditions, between 200 and 550°C in a conventional fixed-bed reactor. The high density of Brønsted acid sites, proved by temperature-programmed desorption (TPD) of ammonia and diffuse reflectance FT-IR of adsorbed pyridine measurements, make H-ZSM-5 zeolite an effective catalyst for DCE decomposition. Vinyl chloride was identified as an intermediate in 250–400°C range. When vinyl chloride was destroyed at higher temperatures, all the zeolites showed a great selectivity (>90%) to HCl. CO was promoted in quantity reflecting the difficulty of its oxidation over these zeolite catalysts. The activity of the zeolites was reduced in the presence of water vapour (15,000 ppmv). It was noticed that the addition of water to the feed stream did not alter the order of activity observed in the dry experiments. Moreover, the presence of water in the DCE decomposition changed significantly the reaction product distribution. Vinyl chloride formation was found to be significantly lowered over the three zeolites, and selectivity to CO2 formation was largely enhanced. The X-ray powder diffraction (XRD) analysis of the deactivated samples indicated partial destruction of the zeolite crystal structure during reaction. 相似文献
20.
《分离科学与技术》2012,47(6):868-876
A green chemical method was explored and described for separation and extraction of the toxic hexavalent chromium from aqueous solutions and real water samples. A green reduction reaction for the transformation of toxic hexavalent chromium into the nontoxic trivalent chromium ion was performed by using hydrogen peroxide. The produced Cr(III) was then extracted by biosorption on the surface of a novel and eco-friendly gelatin-grafted-baker’s yeast (Gelatin-Yeast) biosorbent. The investigated biosorbent was characterized by high capacity value of the reduced trivalent chromium species in pH 6.0 as 1.120 mmol g?1. The biosorption processes were examined, monitored, and optimized in different experimental and controlling parameters. The potential applications of Gelatin-Yeast for separation and removal of Cr(VI) from real industrial and sea water samples were also studied. 相似文献