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Investigation Of Catalytic Activity And Selectivity Of Pd and Ni Loaded Clinoptilolite Rich Natural Zeolite For Citral Hydrogenation/Uçar, Şule. Yılmaz, Selahattin January 2002 (has links)
Thesis (Master)--İzmir Institute of Technology, İzmir, 2002. / Includes bibliographical references (leaves. 92-96).
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Non-oxidative conversion of methane into aromatic hydrocarbons over molybdenum modified H-ZSM-5 zeolite catalystsTshabalala, Themba Emmanuel 02 July 2014 (has links)
Dehydroaromatization of methane (MDA) reaction was investigated over platinum modified
Mo/H-ZSM-5 catalysts which were pre-carbided at 750 oC. The influence of platinum on the
catalytic performance and product selectivity of Mo/H-ZSM-5 catalysts for the MDA reaction at
700 oC was studied. The presence of platinum led to a slight decrease in methane conversion.
As the platinum loading increased, the methane conversion decreased further and the catalytic
stability increased with time-on-stream (TOS) during the MDA reaction. Aromatic selectivities
above 90% were obtained with catalysts containing low platinum loadings (0.5 and 1.0 wt.%),
with benzene being the most prominent product. A decrease in coke selectivity and coke
deposits was noted with the platinum modified Mo/H-ZSM-5 zeolite catalysts.
A comparative study was performed to compare platinum, palladium and ruthenium promoted
Mo/H-ZSM-5 zeolite catalysts with un-promoted Mo/H-ZSM-5. The ruthenium promoted
catalyst proved to be superior in catalytic performance, with a higher methane conversion
obtained than found for platinum promoted and palladium promoted Mo/H-ZSM-5 catalysts.
Benzene selectivity of about 60% was obtained for ruthenium and palladium promoted Mo/HZSM-
5 catalysts and the total aromatic selectivity was maintained at 90%. TGA results showed
a total reduction of 50% by weight of carbon deposited on the promoted Mo/H-ZSM-5 catalyst. Dehydroaromatization of methane was studied over tin modified Pt/Mo/HZSM-5 catalysts and
compared to Pt/Mo/H-ZSM-5 catalyst at 700 oC. Addition of tin decreased the activity towards
methane aromatization. However, the formation of aromatic compounds was favoured. The CO
FT-IR adsorption and CO chemisorption techniques showed that the catalyst preparation method
had an effect on the catalytic performance of tin modified Pt/Mo/H-ZSM-5 catalysts. High
aromatic selectivity and low coke selectivity were obtained with co-impregnated and
sequentially impregnated Pt/Sn catalysts. While a decrease in the formation rate of carbonaceous
deposits is mainly dependent on the availability of platinum sites for the hydrogenation of
carbon. The order of sequentially loading platinum and tin has an effect on the electronic and
structural properties of platinum as shown by XPS and FT-IR studies. CO chemisorption and the
FT-IR adsorption studies showed that addition of tin decreased the adsorption capacity of the
platinum surface atoms. Catalyst preparation methods and successive calcination treatments
affected the location of both tin and platinum atoms in the catalyst. Catalysts prepared by the coimpregnation
method showed a good platinum dispersion, better than found for the sequentially
impregnated catalysts.
The MDA reaction was carried out at 800 oC over manganese modified H-ZSM-5 zeolite
catalysts prepared by the incipient wetness impregnation method. The effect of a number of
parameters on the catalytic performance and product selectivity was investigated, such as
reaction temperature, manganese precursor-type, tungsten as promoter, manganese loading and
use of noble metals. The study of the effect of reaction temperature showed that the methane
conversion increased linearly with increase in reaction temperature from 700 to 850 oC. The selectivity towards aromatic compounds (of about 65%) was attained for the reactions performed
at 750 and 800 oC. Formation rate of carbonaceous deposits increased linearly with increase in
reaction temperature. The use of different manganese precursors to prepare Mn/H-ZSM-5
catalysts had an effect on both the catalytic behaviour and the product distribution. High
catalytic activities were obtained for the catalysts prepared from Mn(NO3)2 and MnCl2 salts.
However, the product distribution was significantly different, with the Mn(NO3)2 catalyst being
more selective towards aromatic compounds while the MnCl2 catalyst was more selective toward
coke. The effect of manganese loading was studied at 800 oC and an optimum catalyst activity was obtained at 2 and 4 wt.% manganese loadings. The aromatic selectivity above 70% and
coke selectivity of 20% were obtained for a 2 wt.% loaded catalyst.
Addition of tungsten as a promoter onto the 2 wt.% loaded catalyst (2Mn/H-ZSM-5) lowered the
catalytic activity but the catalyst remained fairly stable with increase in TOS. Tungsten modified
catalysts favoured the formation of carbonaceous deposits over aromatic compounds. TGA
results showed a coke deposit of 164 mg/g.cat, an 88% increase in coke deposit when tungsten
was used a promoter. Noble metals were added to reduce the total amount of coke on the
tungsten modified Mn/H-ZSM-5 catalysts. The presence of a noble metal favoured the
formation of aromatic compounds and suppressed the formation of coke. Platinum and
ruthenium promoted catalysts were the active catalysts and aromatic selectivity increased from
12% to 55% and 46% respectively. A reduction in the total amount of coke deposit on the
platinum promoted catalyst (42%) and the ruthenium promoted catalyst (31%) was noted.
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Acetyl-nitrate nitration of toluene by zeolite catalysts and methods of oxidation of graphite nanofibersJean-Gilles, Riffard P. January 2007 (has links)
Thesis (M.S.)--Villanova University, 2007. / Chemistry Dept. Includes bibliographical references.
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Selective hydrogenation of acetylene on zeolite-supported bimetallic catalystsHuang, Wei. January 2008 (has links)
Thesis (Ph.D.)--University of Delaware, 2007. / Principal faculty advisors: Jingguang G. Chen and Raul F. Lobo, Dept. of Chemical Engineering. Includes bibliographical references.
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Selective hydrogenation on zeolite-supported bimetallic catalystsHuang, Wei. January 2005 (has links)
Thesis (M.Ch.E.)--University of Delaware, 2005. / Principal faculty advisors: Jingguang Chen, Raul F. Lobo, Dept. of Chemical Engineering. Includes bibliographical references.
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Study of SCR using Cu-Zeolite catalysts on a light-duty diesel engine under steady state and transient conditionsGall, M. January 2015 (has links)
The recognition of the negative impact of NOx resulted in increasingly tighter automotive emission regulations. Companies are under pressure to develop methods, which can meet the legislative demands. After treatment solutions, and especially Selective Catalytic Reduction, became the focus of research and have shown so far promising results. However, more in depth understanding of the SCR process under different conditions is needed. This thesis describes an investigation of the SCR performance using gas and urea injections under steady state and transient conditions undertaken on a light duty diesel engine using a 1D exhaust system designed for uniform flow across the catalyst. Under steady state conditions, the SCR performance was examined for low and high temperature conditions. Ammonia was supplied either as 5% ammonia gas or in form of urea injection. The engine was operating at 1500 rpm and 6 and 8 bar BMEP to provide an exhaust gas temperature of 210 °C and 265 °C respectively. Also, the effect of SCR brick length on the NOx conversion was investigated using SCR catalysts of length 30, 45 and 75 mm. To measure the influence of NO2:NOx ratio on the SCR performance, different sizes of standard DOC were used. NH3:NOx dosage levels included; α~0.5 - deficient ammonia, α~1.0 - stoichiometric ammonia, α~1.25 - excess ammonia. Gas emissions were measured before and after the SCR catalysts with a Horiba FTIR analyser during steady state and long transient tests. It was found that conditions such as temperature and NO2:NOx had the biggest impact on the SCR performance. During the steady state engine conditions, at α~1.0 ammonia dosing and NO2:NOx ratio of 0, only 17% of NO was converted in the first 30 mm of the SCR brick length. The conversion was improved at high temperature (263 °C) to 31%. A fast response CLD analyser was used during short transient testing to sample emissions with a high resolution. The short transient test with standard 0.5 and 1 DOC, and fixed ammonia dosing, showed that NOx conversion was reduced during the ramp event due to deficient ammonia and a drop in the supplied NO2:NOx ratio. During urea injection experiments, urea was injected either through an oblique pipe arrangement with a mixer device placed downstream or directly into a mixing can. In this case the mixer device was replaced with a straight pipe. A 75mm SCR was fitted and to ensure that supplied NO2:NOx ratio was zero, a palladium only DOC was used post a DPF. It was found that a large proportion of urea decomposition and hydrolysis was occurring on the surface of the SCR catalyst. Comparing NOx performance between urea injection and ammonia gas dosing experiment, more NO was converted for a given NH3:NOx ratio when ammonia was supplied in the form of gas. That was true for low and high temperature tests. For most studies, a long 10 degree diffuser was used in front of the SCR to provide uniform gas distribution across the catalyst. In addition SCR performance was investigated with a 180 degree sudden expansion diffuser in order to measure the influence of temperature and velocity profiles. During this study, a 45 mm SCR catalyst was used to provide a moderate amount of NO conversion and ammonia slip. The results showed that the flow and temperature distribution upstream of the SCR catalyst will have an effect on the NOx conversion, and that gas velocity has bigger impact on NOx conversion than gas temperature.
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Low Pressure Catalytic Co-Conversion of Biogenic Waste (Rapeseed Cake) and Vegetable OilGiannakopoulou, Kanellina, Lukas, Michael, Vasiliev, Aleksey, Brunner, Christoph, Schnitzer, Hans 01 May 2010 (has links)
Zeolite catalysts of three types (H-ZSM-5, Fe-ZSM-5 and H-Beta) were tested in the catalytic co-conversion of rapeseed cake and safflower oil into bio-fuel. This low pressure process was carried out at the temperatures of 350 and 400 °C. The yields and compositions of the product mixtures depended on the catalyst nature and the process temperatures. The produced organic phases consisted mainly of hydrocarbons, fatty acids and nitriles. This mixture possessed improved characteristics (e.g. heating value, water content, density, viscosity, pH) compared with the bio-oils, making possible its application as a bio-fuel. The most effective catalyst, providing the highest yield of organic liquid phase, was the highly acidic/wide-pore H-Beta zeolite. The products obtained on this catalyst demonstrated the highest degree of deoxygenation and the higher HHV (Higher Heating Value). The aqueous liquid phase contained water-soluble carboxylic acids, phenols and heterocyclic compounds.
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Oxidant concentration effects in the hydroxylation of phenol over titanium-based zeolites Al-free Ti-Beta and TS-1Burton, Robert M 03 1900 (has links)
Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2006. / This work focuses on the effects of hydrogen peroxide concentration on the catalytic activity
and product selectivity in the liquid-phase hydroxylation of phenol over titanium-substituted
zeolites Al-free Ti-Beta and TS-1 in water and methanol solvents. Hydroquinone is typically
the desired product, and these solvents employed have previously been shown to be of
importance in controlling the selectivity of this reaction.
Different volumetric quantities of an aqueous 30 wt-% peroxide solution were added to either
water or methanol solutions containing the catalyst and phenol substrate, and the reaction
monitored by withdrawing samples over a period of 6-8 hours.
For Al-free Ti-Beta catalysed reactions, the peroxide concentration affects the selectivity and
activity differently in water and methanol solvents. Using methanol solvent, the selectivity to
hydroquinone formation is dominant for all peroxide concentrations (p/o-ratio > 1), and
favoured by higher initial peroxide concentrations (> 1.27 vol-%), where p/o-ratios of up to
can be reached; in water solvent, increasing the peroxide concentration above this level
results in almost unchanging selectivity (p/o-ratio of ca. 0.35). For lower peroxide
concentrations in water, the p/o-ratio increases slightly, but never exceeds the statistical
distribution of ca. 0.5. Using water as a solvent, higher phenol conversion is obtained as the
initial peroxide concentration increases; in methanol the phenol conversion is largely
independent of peroxide concentration.
As expected for the smaller pore TS-1, higher hydroquinone selectivity is obtained in
methanol than for Al-free Ti-Beta, which is consistent with shape-selectivity effects enhanced
by the use of this protic solvent. Interestingly, with TS-1 the p/o-ratio is higher at lower phenol
conversions, and specifically when the initial peroxide concentration is low (p/o-ratio
exceeding 3 were obtained at low phenol conversion), and decreases to a near constant
value at higher conversions regardless of the starting peroxide concentration. Thus, low
peroxide concentrations favour hydroquinone formation when TS-1 is used as the catalyst.
Comparing the performance of the two catalysts using methanol solvent, the phenol
conversion on TS-1 is more significantly influenced by higher hydrogen peroxide
concentrations than Al-free Ti-Beta. However, with higher initial concentrations the
unselective phenol conversion to tars is more severe since the hydroquinone selectivity is not
higher at these high peroxide concentrations. The increased tar formation, expressed as tar
deposition on the catalyst or as the tar formation rate constant, confirms that the greater amount of free-peroxide present is mainly responsible for the non-selective conversion of
phenol.
Kinetic modelling of the reaction data with an overall second-order kinetic model gave a good
fit in both solvents, and the phenol rate constant is independent of changing hydrogen
peroxide concentration for the hydroxylation over Al-free Ti-Beta using water as the solvent
(kPhenol = 1.93 x 10-9 dm3/mmol.m2.s). This constant value suggests that the model developed
to represent the experimental data is accurate. For TS-1 in methanol solvent the rate
constant is also independent of peroxide concentration (kPhenol = 1.36 x 10-8 dm3/mmol.m2.s).
The effect of the method of peroxide addition was also investigated by adding discrete
amounts over a period of 4.5 hours, and was seen to improve hydroquinone selectivity for
reaction on both catalysts, and most significantly for Al-free Ti-Beta in methanol solvent. With
TS-1, the mode of peroxide addition had little influence on phenol conversion, but the initial
selectivity to hydroquinone was ca. 1.6 times higher than for an equivalent single-portion
addition (at a similar phenol conversion). Discrete peroxide addition for hydroxylation in
methanol over Al-free Ti-Beta gave greatly improved hydroquinone selectivities compared to
the equivalent single-dose addition. Compared to TS-1, the initial selectivity was not as high
(p/o-ratios of 0.86 and 1.40 respectively at 10 mol-% phenol conversion), but this can be
explained on the basis of geometric limitations in the micropores of TS-1 favouring
hydroquinone formation. The final selectivity, however, is marginally higher (using the same
mode of peroxide addition, and at the same phenol conversion).
Discrete peroxide addition has an additional benefit in that it also reduces the quantity of
free-peroxide available for product over-oxidation, and consequently reduces the amount of
tars formed.
Thus, the interaction of the effects of peroxide concentration and the solvent composition and
polarity on the product selectivity and degree of tar formation is important. Particularly with
TS-1, lower peroxide concentrations in bulk methanol solvent are highly beneficial for
hydroquinone formation, because of the implicit geometric constraints in the micropores, the
lower water concentration, and the decreased tar formation associated with high methanol
concentrations. This could have significant reactor design implications, as the results
obtained here suggest that the reaction should be terminated after approximately 30 minutes
to maximise hydroquinone production (under the conditions evaluated in these experiments),
even though the corresponding phenol conversions are low (ca. 10 mol-%). The higher
hydroquinone selectivities reached at low phenol conversions for the discrete peroxide
addition experiments also confirm this. Practically, to enhance the hydroquinone selectivity for reaction over TS-1, the initial phenol-peroxide molar ratio should be ca. 10, methanol
should constitute not less than 90 vol-% of the reaction volume, and the peroxide should be
added in discrete amounts.
For reaction over Al-free Ti-Beta, methanol solvent also enhances the hydroquinone
formation as expected. At low phenol conversions (ca. 10 mol-%) hydroquinone is still the
preferred product, although in contrast to TS-1 the selectivity increases with phenol
conversion, and is higher with higher initial peroxide concentrations. Under the best
conditions evaluated here for optimal hydroquinone formation, the initial phenol-peroxide
molar ratio should be ca. 2.5, with methanol making up at least 90 vol-% of the total volume.
Discrete peroxide addition in methanol solvent for the Al-free Ti-Beta catalysed hydroxylation
gives excellent improvements in hydroquinone selectivity (2.5 times higher than water
solvent), and the addition in more discrete portions might further improve hydroquinone
formation, and should therefore be examined.
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Performance of zeolite ZSM-5 synthesised from South African fly ash in the conversion of methanol to hydrocarbonsFolifac, Leo January 2018 (has links)
Thesis (Master of Engineering in Chemical Engineering)--Cape Peninsula University of Technology, 2018. / Zeolites have found applications as heterogeneous or solid catalyst in the petrochemical and refining industries. Zeolite ZSM-5 in particular is a highly siliceous solid catalyst with a porous network that consists of medium pore structure (pore openings 5-5.5 A). The solid catalyst (ZSM-5) is well known for its high temperature stability and strong acidity, which makes it an established catalyst used for different petrochemical processes such as Methanol-To-Gasoline (MTG), isomerisation, disproportionation, and cracking. Unlike in the past, the synthesis of zeolite ZSM-5 from other sources that contains silica (Si) and alumina (Al) with the addition of a template (TPBr) as a structure-directing agent is eminent. Its synthesis can be achievable from coal fly ash that is a waste material and a cheap source of Si and Al. Coal fly ash is a waste material that is produced during the combustion of coal to generate electricity. The elemental composition of coal fly ash consists of mostly SiO2 and Al2O3 together with other significant and trace elements. Zeolite ZSM-5 catalyst synthesised from coal fly ash by previous authors required an excessive amount of additional source of silica even though the XRD spectra still show the presence of quartz and mullite phase in the final products. These phases prevented the use of fly ash (solid) as a precursor to synthesise zeolite ZSM-5 products. However, the synthesis of high purity zeolite ZSM-5 products by extracting silica and alumina from South African fly ash and then using it with small amounts of fumed silica was investigated This aim was achieved by fusing fly ash (FA) with sodium hydroxide (NaOH) under hydrothermal condition set at 550 oC for 1 hour 30 minutes. The quartz and mullite phase observed by previous authors was digested by the fusion process. Thereafter, the treatment of fused fly ash filtrate (FFAF) with concentrated H2SO4 (98-99%), precipitated silica and removed Al that therefore increased the Si/Al ratio from 1.97 in fly ash (FA) to 9.5 in the silica extract (named fused fly ash extract). This route was designed to improve the quality of the final products and reduced the amount of fumed silica added to the synthesis mixture prior to hydrothermal synthesis. In this line of investigation, the process of adding fumed silica to the hydrothermal gel was optimised. H-FF1 with a Si/Al ratio of 9.5 was synthesised using the silica extract without the addition of fumed silica. Its XRD, SEM and relative crystallinity results proved that H-FF1 was inactive and hence was not further characterised and utilised in the conversion of methanol to hydrocarbons (MTH). Purer phase zeolite ZSM-5 products (H-FF2 and H-FF3) that were synthesised from silica extract with the addition of small amounts of fumed silica were characterised and successfully used in the methanol to hydrocarbons (MTH) reaction. The synthesised ZSM-5 products had different Si/Al ratio, different morphology, crystal size, BET surface area, and relative crystallinity as well as different trends in the MTH reaction. It was also observed that H-FF2 and H-FF3 (pure phase) solid catalyst deactivated faster than the commercial H-ZSM-5 in the MTH reaction. However, the MTH conversion over H-FF2 competed with that of the commercial H-ZSM-5 within 3 hours of time on stream (TOS) but later deactivated at a faster rate. This was caused by the large crystal size and reduced BET surface area of H-FF2 when compared to the commercial H-ZSM-5. However, H-FF2 performed better than H-FF3 on stream (MTH reaction) due to its smaller crystal size and higher BET. This study has successfully utilised a route that synthesised high purity zeolite ZSM-5 products from the South African fused fly ash extract (FFAE) with the addition of small amounts of fumed silica. The properties of the synthesised zeolite ZSM-5 products (H-FF2 and H-FF3) were similar to that of the commercial H-ZSM-5 as well as active in the MTH reaction. This promoted the utilisation of a waste material (coal fly ash) to synthesise highly siliceous zeolite ZSM-5 products that avoided the presence of mineral phases from fly ash in the final products.
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Sensing, separations and artificial photosynthetic assemblies based on the architecture of zeolite Y and zeolite LWhite, Jeremy C. January 2009 (has links)
Thesis (Ph. D.)--Ohio State University, 2009. / Title from first page of PDF file. Includes bibliographical references (p. 268-291).
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