Search

The “ one-pot ” hydrolyltic hydrogenation of cellulose towards C2-C6 sugar alcohols has been recognized as one of the most promising biomass valorization routes for the production of high added-value chemicals. In this work, we studied the performance of Ru and Pt catalysts supported on micro/mesoporous activated carbon, in the hydrolytic hydrogenation of microcrystalline and ball-milled cellulose, in neat water, at 180 °C and at relatively low hydrogen pressure of 2 MPa. The impact of metal loading (1–5 wt.%), metal reduction method (H 2 at 350 °C or NaBH 4 ) and acidification (sulfonation) of the AC support on cellulose conversion and selectivity to the various products were systematically addressed. It was shown that Pt is significantly more selective towards hexitols (sorbitol and mannitol) compared to Ru, in glucose-rich reaction media, such as those offered by the easily hydrolyzed ball-milled cellulose. For example, the 5wt%Pt/AC-SO 3 H catalyst afforded hexitols yield of 69.5 wt.% (at 96.1% conversion) compared to 10.9 wt.% (at 95.2% wt.% conversion) obtained by the corresponding Ru catalyst, the latter being also selective towards glycerol and propane-1,2-diol (propylene glycol). A relatively moderate metal loading, such as in 3 wt.%Ru/AC-SO 3 H, was more favorable for hexitols production (44.5 wt.% yield, at 94.8 wt.% conversion) with Ru catalysts. These results were also verified by glucose hydrogenation experiments that were conducted at the same experimental conditions. Both Pt and Ru exhibited relatively high glucose hydrogenation activity towards hexitols, versus retro-aldol reactions that lead directly to smaller C2–C4 compounds, while the difference in the final product yields between the two metals was attributed to the higher hexitols hydrogenolysis (C C cleavage) reactivity of Ru. HRTEM data showed the formation of metallic crystalline Pt and Ru nanoparticles (≤4 nm, depending on loading) as well as of amorphous oxygen-rich M(O) x δ+ phases, which were also confirmed by the XPS data. The presence of these phases which may be a source of acidity, as well as the bacisity of the parent AC used in this study, were mainly responsible for inducing isomerization, retro-aldol and dehydration reactions leading eventually to increased glycerol and propylene glycol selectivity, as was observed for both low-metal catalysts, i.e. 1 wt.% Pt or Ru/AC.

The thermal and catalytic fast pyrolysis of biomass aims at the production of pyrolysis oil (bio-oil), which can be utilized as a source of chemicals or as a bio-crude for the production of hydrocarbon fuels. We investigated low-cost, naturally derived basic MgO materials as catalysts for the catalytic fast pyrolysis of lignocellulosic biomass as alternatives to classical acidic zeolite catalysts. The MgO catalysts were produced from natural magnesite mineral without any significant treatment besides calcination, crushing and sieving. Their structure, composition, porosity, morphology and surface properties were thoroughly examined by XRD, XRF, N 2 porosimetry, SEM, TEM, TPD-CO 2 and TPD-NH 3 . The physicochemical characteristics of the MgO catalysts depended mainly on the different production conditions (duration and temperature of calcination). Despite their negligible acidity, the MgO catalysts effectively reduced the oxygen content of the produced bio-oil and exhibited similar or even better performance compared to that of an industrial ZSM-5 catalyst formulation ( i.e. non-catalytic pyrolysis: 38.9 wt.% organic bio-oil with 38.7 wt.% O 2 ; ZSM-5 based catalyst: 20.7 wt.% organic bio-oil with 30.9 wt.% O 2 ; selected natural MgO catalysts: 25.7 wt.% organic bio-oil with 31.0 wt.% O 2 or 21.1 wt.% organic bio-oil with 28.4 wt.% O 2 ). The basic sites of the MgO catalysts favored reduction of acids and deoxygenation via ketonization and aldol condensation reactions, as indicated by the product distribution and the composition of the bio-oil. Oxygen was removed mainly via the preferred pathway of CO 2 formation, compared to CO and water as in the case of ZSM-5 zeolite. On the other hand, reaction coke slightly increased over the MgO catalysts as compared to ZSM-5; however, the MgO formed coke was oxidized/burnt at significantly lower temperatures compared to that of ZSM-5, thus enabling MgO regeneration by relatively mild calcination in air. A systematic correlation of product yields and oxygen content of bio-oil with the physicochemical properties of the MgO catalysts has been established.

Isomerization of glucose to fructose is an important reaction with numerous applications in terms of biomass valorization. The reaction is catalyzed enzymatically but may also proceed under alkaline conditions, in which case it is accompanied by low selectivity and formation of byproducts. Solid Lewis acid and basic catalytic materials are being studied as alternative catalysts. In this work, the isomerization of glucose to fructose in aqueous media over homogeneous and heterogeneous catalysts has been investigated. The effect of polar aprotic solvents and their mixtures with water on glucose conversion and fructose selectivity was also studied. Sodium aluminate (NaAlO2) has been proven to be very effective, resulting in high fructose yield (52.1 %) and high selectivity (84.8 %). Among the various solid catalysts tested, MgO afforded glucose conversion of 44 %, with 75.8 % and 33.4 % fructose selectivity and yield, respectively, when the isomerization reaction was conducted in neat H2O.

In the present work we studied the hydrogenation/hydrogenolysis of d -glucose over Pt and Ru catalysts supported on activated micro/mesoporous carbon (AC), under low hydrogen pressure (1.6 MPa) and relatively high reaction temperature, i.e. 180 °C. We also studied the effect of metal content (1–5 wt.%), method of metal pre-treatment/reduction (H 2 at 350 °C or NaBH 4 ) and reaction time (1–12 h). All the Ru and Pt/AC catalysts were very active (conversion ≥97%) with the Pt/AC catalysts being also very selective toward sorbitol (sel. ≥90%) irrespective of metal content, method of reduction and reaction time (up to 12 h). On the other hand, the Ru/AC catalysts exhibited a wide range of sorbitol selectivity values (55–93%) having various C 3 –C 6 sugar alcohols (1,2,5,6-hexanetetrol, arabinitol, threitol, glycerol and 1,2-propanediol) as main by-products. The formation of by-products was dependent on the crystalline/amorphous nature of Ru and Ru(O) x δ + nanoparticles which were in turn affected by the Ru content and the method of reduction.

This study investigates the effect of active metal and the nature and pre-treatment of the support in a series of K-promoted NiMo catalysts supported on activated carbon (AC) for the hydrogenation reaction of CO. The Ni Mo synergistic effect was found to be essential for the activation of CO. The use of activated carbon as support led to a three-fold increase in the selectivity toward higher alcohols, compared to the unsupported material, probably due to a reduction in the crystallinity of the active NiMoO4 phase and its partial transformation from alpha to beta form. Pre-treatment of the activated carbon prior to its use as support with HNO3 aqueous solution led to significant increase in CO conversion, related to the lower amount of ash and the much higher acidity of the acid treated sample. The use of a higher surface area acid-treated support also increases activity, with the K NiMo/AC2a catalyst exhibiting a 45% higher conversion at 280 °C compared to K NiMo/AC1a. The improvement in activity can be ascribed to better dispersion of the active phase on the higher surface area AC support and therefore higher exposure of active Ni O Mo sites. Overall, the K NiMo/AC2a catalyst exhibited the optimum performance, with high CO conversion (25% at 280 °C) and high production of oxygenates, with a space time yield to oxygenates of 141.5 mg/gcatalyst/h at 280 °C. A clear tendency of increasing higher alcohol production with decreasing acidity was evidenced for all K-promoted bimetallic NiMo catalysts.

The valorization of various types of low-quality vegetable oils with relatively high content of free fatty acids (FFA) is a research field of increased interest. The esterification of oleic acid, a highly abundant FFA in waste oils, with trimethylolpropane (TMP) towards the production of the corresponding triesters, which can be used in lubricants or hydraulic fluids, was studied in this work. The catalysts tested were various meso/macroporous oxides, such as ZrO2, 3.5%SiO2-ZrO2, SiO2-Al2O3, SBA-15 and Al-SBA-15 with varying textural and acidic properties and the corresponding supported heteropoly acid catalysts, prepared by the use of phosphotungstic (H3PW12O40) and tungstosilicic (H4SiW12O40) acids. The catalysts were characterized by ICP-AES, XRD, FT-IR, N-2 porosimetry and FT-IR coupled with pyridine adsorption. The main product at 200 degrees C and after 6 h of reaction was the triester (TE) of oleic acid with selectivity values ranging from 85% to 99% at conversion degrees of 82% to 96%. The two aluminosilicate catalysts that combine Bronsted and Lewis acidity (i.e. SiO2-Al2O3 and Al-SBA-15) showed slightly higher yields of triester (similar to 83%) compared to the rest oxides (similar to 78%), while the Bronsted acidity induced by the two heteropoly acids, especially by PW, provided very high reactivity and selectivity towards triesters, irrespective of the type of support used, reaching triester yield values of 95% (96.2% conversion, 98.7% selectivity) with the 20%PW/ZrO2 catalyst, The most stable catalysts against leaching of heteropoly acids were those supported on 3.5%SiO2-ZrO2 and SiO2-Al2O3. (C) 2017 Elsevier B.V. All rights reserved.

The transformation of α-limonene into p -cymene over oxide catalysts (γ-Al 2 O 3 , TiO 2 , SiO 2 , MCM-41) has been studied under H 2 and He atmosphere in the temperature range 200–300 °C using a fixed bed micro-reactor working under atmospheric pressure. The catalysts were characterized using various physicochemical techniques (N 2 adsorption–desorption, NH 3 -TPD, XRD, TPR, HR-TEM). We demonstrated that an almost complete transformation of α-limonene into p -cymene can be obtained at 300 °C over a high surface area anatase (Alfa Aesar) in helium atmosphere. The high surface area titania was also proved a very stable catalyst. The high catalytic performance of this oxide could be attributed to a good balance between the acidity and surface reducibility exhibited by this material. The aforementioned properties are, respectively, relevant to the isomerization and disproportionation/dehydrogenation steps involved in the mechanism of title reaction. Based on the yields obtained for p -cymene and by-products we proposed a mechanistic scheme for the title reaction over the high surface area titania.

Supported Ir, Pd, Rh and Ru catalysts were examined for the conversion of glucose and cellulose in water in the presence of hydrogen. The catalysts were prepared by incipient wetness impregnation of a BEA zeolite (SiO2/Al2O3 = 21.6, Ssp = 739 m2/g) with acetylacetonate metal precursors. Among these catalysts, Ru-BEA was found to be the most active for the conversion of cellulose, while Ir-BEA was found to be the most selective for the formation of sorbitol. Thus, the highest yield to sorbitol was found in the presence of 3 wt%Ru/BEA catalyst irrespective of the raw material nature (glucose or cellulose). It corresponded to a value of 22% for the conversion of the commercial cellulose, and of 72.8% for the conversion of glucose. The Ru-BEA catalyst was followed by the 3 wt%Ir-BEA that led to a yield of 55.3% for glucose and 22% for cellulose but to a much higher selectivity, i.e. over 99.9% for glucose and 89.2% for cellulose. While the high selectivity of Ir to sorbitol was correlated with the d-band width of the metal, the high activity of Ru for the cellulose conversion was assigned to the generation of H+ and [Ru(H2O)5OH]2+ as Bronsted acids by Ru species in water. Finally, the addition of pure nanoscopic hydroxylated SnF4 to the 3 wt%Ir-BEA catalyst led to a conversion of cellulose of almost 99% after only 3 h with a selectivity to sorbitol of 72.5%.

Adsorption of 4,6-dimethyldibenzothiophene (4,6-DMDBT) from solutions in hexadecane was investigated on three commercial nanoporous activated carbons of different origin and nature, which possessed either microporous or combined micro/mesoporous structures, and their oxidized counterparts. The initial and exhausted carbons were characterized using the nitrogen porosimetry at 77 K, thermal analysis, Boehm titration, and FTIR. The capacity for 4,6-DMDBT removal increases with an increase in the volume of pores with size similar to that of 4,6-DMDBT molecules, which is about 6 A. Functional groups present on the surface of larger pores contribute to adsorption via polar interactions.

The main objective of the present work was the evaluation of commercial ZSM-5 catalysts (diluted with a silica–alumina matrix) in the in situ upgrading of lignocellulosic biomass pyrolysis vapours and the validation of their bench-scale reactor performance in a pilot scale circulating fluidized bed (CFB) pyrolysis reactor. The ZSM-5 based catalysts were tested both fresh and at the equilibrium state, and were further promoted with cobalt (Co, 5% wt%) using conventional wet impregnation techniques. All the tested catalysts had a significant effect on product yields and bio-oil composition, both at bench-scale and pilot scale experiments, producing less bio-oil but of better quality. Incorporation of Co exhibited no additional effect on water or coke production induced by ZSM-5, compared to non-catalytic fast pyrolysis. On the other hand, Co addition significantly increased the formation of CO2 compared to the CO increase which was favored by the use of ZSM-5 alone. These changes in CO2/CO yields are indicative of the different decarbonylation/decarboxylation mechanism that applies for Co3O4 compared to ZSM-5 zeolite, due to the differences in their acidic properties (mainly type of acid sites). Co-promoted ZSM-5 catalysts simultaneously enhanced the production of aromatics and phenols with a more pronounced performance in the pilot-scale experiments resulting in the formation of a three phase bio-oil, rather than the usual two phase catalytic pyrolysis oil (aqueous and organic phases). The third phase produced is even lighter than the aqueous phase and consists mainly of aromatic hydrocarbons and phenolic compounds. Addition of Co in ZSM-5 is thus suggested to strongly enhance aromatization reactions that result in selectivity increase towards aromatics in the bio-oil produced. Possible routes of catalyst deactivation in the pilot plant's continuous operation process have been suggested and are related to pore blocking and masking of acid sites by formed coke (reversible deactivation), partial framework dealumination of the fresh zeolitic catalyst, and accumulative ash deposition on the catalyst that depends on the nature of biomass (content of ash).

The main objective of the present work was the study of different ZSM-5 catalytic formulations for the in situ upgrading of biomass pyrolysis vapors. An equilibrium, commercial diluted ZSM-5 catalyst was used as the base case, in comparison with a series of nickel (Ni) and cobalt (Co) modified variants at varying metal loading (1–10 wt.%). The product yields and the composition of the produced bio-oil were significantly affected by the use of all ZSM-5 catalytic materials, compared to the non-catalytic flash pyrolysis, producing less bio-oil but of better quality. Incorporation of transition metals (Ni or Co) in the commercial equilibrium/diluted ZSM-5 catalyst had an additional effect on the performance of the parent ZSM-5 catalyst, with respect to product yields and bio-oil composition, with the NiO modified catalysts being more reactive towards decreasing the organic phase and increasing the gaseous products, compared to the Co 3 O 4 supported catalysts. However, all the metal-modified catalysts exhibited limited reactivity towards water production, while simultaneously enhancing the production of aromatics and phenols. An interesting observation was the in situ reduction of the supported metal oxides during the pyrolysis reaction that eventually led to the formation of metallic Ni and Co species on the catalysts after reaction, which was verified by detailed XRD and HRTEM analysis of the used catalysts. The Co 3 O 4 supported ZSM-5 catalysts exhibited also a promising performance in lowering the oxygen content of the organic phase of bio-oil.

A series of C 60 catalysts supported on MCM-41 was prepared in the context of developing a highly active heterogeneous catalytic system for the singlet oxygen-mediated oxidation of organic substrates. Successive incipient wetness impregnation was used for preparing 3, 6, 9 and 12 wt.% C 60 onto MCM-41 surface. N 2 adsorption, FT-IR, XRD, HR-TEM, DRS and TGA, have been used to characterize the photocatalysts. It was found that C 60 is highly dispersed (especially in the 3 and 6 wt.% C 60 catalysts) within the mesopores or on the external surface of MCM-41, as clusters or crystallites/aggregates of very small size and presumably in the form of atomic layers. The mesoporous structure and characteristics (surface area, mesopore size and volume) of MCM-41 remain almost intact upon deposition of C 60 on its surface. The photocatalytic activity was assessed in the photocatalytic oxidation of olefins via the singlet oxygen ene reaction by studying the photooxygenation of 2-methyl-2-heptene as a probe reaction. The catalytic tests were carried out at 0–5 °C in CH 3 CN under oxygen atmosphere and using a 300 W xenon lamp as the light source. To investigate further the potential applications of our catalysts we examined various types of photooxidations including the [4 + 2] or [2 + 2] cycloaddition, the heteroatom oxidation with sulfur or phosphorus containing compounds and the oxidation of phenols. The heterogeneous photocatalysts obtained were proved to be very active exhibiting higher substrate conversion, TON and TOF values, compared to those of the unsupported (solid) C 60 and the corresponding photocatalysts supported on silica or γ-alumina. This was mainly attributed to the better dispersion of C 60 on the MCM-41. The conversion achieved over the catalysts increases with the amount of the supported C 60 up to a value of 6 wt.% and then it decreases whereas the TON and TOF values decrease monotonically as the amount of the supported C 60 increases following the increase in the size of the supported C 60 crystallites/aggregates. Shadow effects were not observed under our experimental conditions.

BACKGROUND: Water-soluble reactive azo dyes are the most problematic dye house effluents, as they tend to pass through conventional treatment systems unaffected. The release of these compounds into the environment is undesirable and their removal becomes environmentally important. In this work, synthesis, characterization and sorption properties of hydotalcite-like compounds (Mg/Al and Mg/Fe), calcined and uncalcined, were investigated for the removal of the reactive azo dye Remazol Red 3BS. RESULTS: The calcined compounds present higher surface area than the uncalcined. The optimum pH for sorption was found to be 6. Thermodynamic analysis reveals that the sorption is spontaneous and endothermic. Equilibrium data were fitted by a Langmuir model, and kinetic data by a second-order model. The calcined Mg/Al compound showed the highest sorption capacity, at 0.125 mmol g−1. Regeneration of dye loaded derivative is achieved using the surfactant SDS. CONCLUSIONS: The prepared hydotalcite-like compounds and especially calcined Mg-Al exhibited significant adsorption capacity, kinetics, and regenerative ability. Its potential applicability as sorbent should be tested in a large-scale implementation. Copyright © 2011 Society of Chemical Industry

In the present work we studied the N2O decomposition activity of nano-Ru/-Al2O3 catalysts prepared by in situ reduction with ethylene glycol (EG), in comparison to catalysts prepared via typical incipient wetness procedure. The metal content, particle size, dispersion and reduction characteristics of the supported Ru catalysts were studied by means of ICP-AES, XRD, HRTEM, TPR-H2 and TPD-H2. The EG reduction method favored the formation of almost spherical metallic Ru nanoparticles with the size of 1–3 nm (HRTEM) and dispersion of 70–35% (TPD-H2), at Ru loading levels of 0.4–1 wt.%. The impregnatedcalcined catalysts exhibited larger Ru nanoparticles (10–80 nm, TEM) with very low degree of dispersion (∼10%). The activity of the EG-prepared catalysts for the decomposition of N2O in oxygen rich feeds and in the absence or presence of NO, H2O, SO2, CO and CO2, was significantly higher compared to that of the impregnated-calcined samples and comparable with that of the most active catalytic systems reported in the literature for the treatment of combustion processes off-gases. The superior activity of the former catalysts, especially of the sample with low Ru content (0.4 wt.% Ru, 1–2 nm particle size), was attributed both to the high dispersion of Ru (70% dispersion), i.e., the high surface area of Ru metal available for reaction, and to the higher intrinsic activity and lower apparent activation energy of the very small supported Ru nanoparticles prepared by the EG reduction method. The EG-prepared nano-Ru/-Al2O3 catalysts could retain their high N2O decomposition activity (higher than 90%) for long time-on-stream by applying intermediate, short term regenerations in reducing atmosphere at moderate temperatures (i.e., 500

The effect of the pretreatment (inert, oxidative, and reducing) of Ru/γ-Al 2 O 3 catalyst on its activity and stability in the decomposition of N 2 O in the absence or presence of O 2 , SO 2 , H 2 O and NO X was studied in the present work. Decomposition of pure N 2 O was slightly enhanced by the H 2 -pretreated catalyst (metallic Ru) compared to the O 2 - or He-pretreated ones, owing to a cyclic oxidation–reduction pathway of metallic Ru. The observed decrease of activity by O 2 or H 2 O addition was reversible compared to SO 2 which caused a strong, irreversible deactivation of the catalyst, irrespective of the type of pretreatment. This was attributed to the formation of stable sulphates, mainly those on RuO 2 surface, which could only be removed by regeneration under reducing (H 2 in He) atmosphere at temperatures of ca. 500 °C. Oxidative or inert regeneration required very high temperatures (i.e. >700 °C) in order to decompose these sulphates. A method of retaining N 2 O conversion activity very high (≥98%) for long reaction times is suggested and is based on frequent and short-time (ca. 10 min) regenerations of the catalyst under reducing atmosphere (ca. 5% H 2 in He). The effect of co-feeding various reducing agents, such as CO or C 3 H 6 , on the N 2 O conversion activity in the presence of O 2 , SO 2 , H 2 O and NO X is negligible, mainly because they are oxidized at relatively low temperatures in the O 2 -rich feeds used in this study.

The structural characteristics and the performance of vanadia catalysts (0.7–8 wt.% V) supported on mesoporous (MCM-41, HMS, MCF, SBA-15), microporous (silicalite) and non-porous (SiO 2 ) silicas in oxidative dehydrogenation of propane were investigated. The structure of vanadia species, the redox and the acidic properties of the catalysts were studied using in situ Raman spectroscopy, TPD- NH 3 and H 2 -TPR. The only vanadia species detected on the surface of HMS and MCM-41 for V loadings up to 8 wt.% were isolated monovanadates indicating high vanadia dispersion. Additional bands ascribed to V 2 O 5 nanoparticles were evidenced in the case of SBA-15 and MCF supported catalysts while these bands were the only ones identified on the surface of the catalysts supported on silicalite and non-porous silica. The catalysts supported on mesoporous HMS and MCM-41 materials showed the best performance achieving high propane conversions (35–40%) with relatively high propene selectivities (35–47%). Lower activity due to the lower degree of vanadia dispersion, caused by the partial destruction of the pore structure was observed for the SBA-15 and MCF supported catalysts. The degree of dispersion of the V species on the catalyst surface and not the pore size and structure of the mesoporous support or the acidity/reducibility characteristics mainly determine the catalytic activity towards propene production. In addition, it was shown that the pore structure and size of the mesoporous supports did not have any significant effect in the turnover rates (TOF values) of propane conversion (and propene formation at low propane conversion, below ca. 10%). However, the highest propene yield (up to 19%) and stable catalytic behavior was attained for catalysts supported on HMS mesoporous silica, and especially for those combining framework mesoporosity and textural porosity (voids between primary nanoparticles).

Well defined layered-double hydroxides (LDH: Mg3Al–NO3/CO3, Mg3Ga–NO3/CO3, Zn2Al–NO3/CO3 and Zn2Ga–NO3/CO3) were prepared using typical procedures starting from Mg(NO3)2·6H2O, Zn(NO3)2·6H2O, Al(NO3)3·9H2O and Ga(NO3)3·H2O. Rh-TPPTS complex was prepared by simple complexation of a Rh precursor [Rh(cod)Cl]2 and TPPTS (3,3′,3″-phosphanetriyl benzenesulfonic acid) in water. The heterogeneization of the Rh-TPPTS complex was performed by anionic exchange between Rh-complex and LDH supports. The catalysts’ structures and the chemical composition were confirmed by chemical analysis, XRD patterns, XP, FTIR and DRIFT spectroscopy. LDH-substituted Rh-TPPTS heterogeneous catalysts showed good catalytic activity in the 1,4-addition of arylboronic acid to 2-cyclohexen-1-one.

The effect of the textural properties and morphology of zeolite Y, used as support of iron (Fe) or cobalt (Co) oxides, on the quantity and quality of the multi-wall carbon nanotubes (MWNTs) synthesized by catalytic chemical vapour deposition (CCVD) of acetylene was studied. The parent zeolite Y was modified by various dealumination procedures, namely hydrothermal treatment (steaming), treatment with ammonium hexafluorosilicate (AHFS) and combined steaming-AHFS. The ion-exchange and wet impregnation methods were used for supporting the metals on the zeolite Y samples, with the latter method providing the most effective catalysts for carbon nanotube (CNT) formation. Severe dealumination of zeolite-Y by steaming, which induced the formation of secondary meso/macropores and of relatively large particles/aggregates, resulted in significant decrease in the formation of CNTs compared to the catalysts based on the parent zeolite-Y. Post-treatment of the steamed samples with AHFS had no beneficial effect on the catalysts' activity. Moderate dealumination of the parent zeolite Y by AHFS also inhibited the formation of CNTs, but to a lesser extent compared to the catalysts based on steamed zeolite Y. The TGA studies revealed the presence of carbon phases with different thermal stability in the zeolite-CNT composites, ranging from amorphous carbon to well-graphitized MWNTs. TEM images and micro-Raman spectra taken right after growth confirmed the formation of high quality MWNTs with a low degree of disorder irrespective of the catalysts used, the degree of dealumination of the zeolite Y and the textural and morphological characteristics of the zeolitic support. (c) 2007 Elsevier Inc. All rights reserved. Microporous and Mesoporous Materials

The present study focuses on the synthesis and characterization of vanadia catalysts supported on non-porous (SiO2), microporous (silicalite), mesoporous (MCM-41, HMS, SBA-15) and ultra-large mesoporous (MCF) silicate materials. The structure and porosity characteristics of the above mesoporous supports were verified by means of XRD, N2 porosimetry and HR-TEM studies. Vanadium was introduced in the porous materials via wet impregnation of vanadium oxalate complex in strongly acidic aqueous media. No crystalline V2O5 phases were found on the surface of all the above mesoporous supports for V loadings as high as 8 wt.%, in contrast to microporous zeolite silicalite and non-porous SiO2 on which V2O5 crystals were formed as evidenced by XRD. Increasing addition of vanadium under the strongly acidic impregnation conditions followed by typical calcination of the catalyst, resulted in partial structure breakdown and loss of surface area of the mesoporous supports which was more pronounced in the case of SBA-15 and MCF materials. The most active catalysts for the formation of propene in the oxidative dehydrogenation of propane (ODP) at reaction temperatures 500–600 °C were those supported on HMS and MCM-41 mesoporous materials showing high propene yields up to 19% at about 600 °C. The vanadia catalysts based on SBA-15 and MCF were less active in the production of propene (yields up to 13%) compared to the MCM-41 and HMS based catalysts. The SiO2 and silicalite based catalysts showed much lower yields of propene (

The ethylene epoxidation activity of Ag catalysts supported on non-porous SiO 2 , microporous silicalite zeolite and mesoporous MCM-41 and HMS silicates was investigated in the present study in comparison to conventional low surface area α-Al 2 O 3 based catalysts. The MCM-41 and HMS based catalysts exhibited similar ethylene conversion activity and ethylene oxide (EO) selectivity with the SiO 2 and α-Al 2 O 3 based catalysts at relatively lower temperatures (up to ∼230 °C), whereas their activity and selectivity decreased significantly at higher temperatures (≥300 °C). The silicalite based catalyst was highly active for a wide temperature range, similar to the SiO 2 and α-Al 2 O 3 based catalysts, but it was the less selective amongst all catalysts tested. High loadings of Ag particles (up to ca. 40 wt.%) with medium crystallites size (∼20–55 nm) could be achieved on the mesoporous materials resulting in very active epoxidation catalysts. The HMS-type silicate with the 3D network of wormhole-like framework mesopores (with average diameter of ∼3.5 nm), in combination with a high-textural (interparticle) porosity, appeared to be the most promising mesoporous support.

Cu-exchanged ZSM-5 zeolites finely coated with CeO2 nanoparticles were tested in this work as catalysts for the selective catalytic reduction (SCR) of NO with C3H6. The CeO2 coated Cu/ZSM-5 shows lower maximum NO conversion activity compared to the non-coated Cu/ZSM-5 catalyst at relatively high temperatures (ca. 450 8C) but the former catalyst is significantly more active at lower temperatures (ca. 350 8C), especially at lower space velocities, both under dry and wet feed conditions. Under simultaneous addition of both SO2 and water in the feed, the beneficial effect of the CeO2 coating at lower reaction temperatures was retained only at low space velocities. The same Cu/ZSM-5 based samples were evaluated as fluid catalytic cracking (FCC) catalytic additives for the in situ reduction of NOx formed during regeneration of the coked FCC catalyst. The amounts of NO and CO emitted during regeneration of the spent FCC catalyst at 700 8C in the presence of Cu/ZSM-5 based additives were compared with those obtained when a commercial CO promoter was used in the FCC catalyst inventory. All Cu/ZSM-5 additives exhibited significant NO reduction ability, which was further enhanced by increasing the Cu loading or the amount of additive in the FCC catalyst. The CeO2coated sample reached the highest deNOx performance (up to 78% NO reduction); however, all additives presented insufficient activity for CO oxidation. Simultaneous NO reduction and CO oxidation was achieved only when the CeO2-Cu/ZSM-5 additive was promoted with Rh or when the non-promoted additives were combined with a commercial CO promoter. Preliminary studies suggested that the Rh-promoted CeO2-Cu/ZSM-5 additives can be very effective for both NO reduction by CO and CO oxidation at certain O2 concentrations, such as in the O2-deficient zones of the FCC regenerator. Further studies are in progress in order to elucidate the reaction mechanism and optimize the additive’s formulation. # 2007 Elsevier B.V. All rights reserved.

This work is a systematic review of the literature over the past decade of the application of activated carbon (microporous or mesoporous) as adsorbents for the removal of heavy metals, focusing especially on lead (Pb) and arsenic (As) ions from the aqueous phase. Classical examples from our lab are also given. Activated carbon is known to provide a high surface area for adsorption. Generally, surface modification is typically required, such as oxidation, treatment with ammonia or even impregnation with ferric ion, etc. and the adsorbent material may originate from various sources. The pristine materials, after modification and those after batch-wise adsorption, were characterized by available techniques (BET analysis, Fourier transform infrared spectroscopy, scanning electron microscopy, thermal analyses, X-ray photoelectron spectroscopy). Adsorption isotherms, thermodynamics and kinetics of the process are also discussed. Selected studies from the literature are examined in comparison with other adsorbents. The role of chemistry in the metals adsorption/removal was investigated.

Aluminosilicate mesostructures (MSU-S BEA ) assembled from zeolite Beta (BEA) seeds exhibited relatively high hydrothermal stability and were significantly more active in the cracking of gas–oil compared to MCM-41 after severe steaming pretreatment. The MSU-S BEA mesoporous materials with wormhole framework structure and those having morphology of solid nanoparticles with high interparticle mesoporosity were more steam-stable and more active after severe steaming than those with hexagonal pore structure. Differences in acid sites strength between the MSU-S BEA materials and MCM-41 could not be probed by the complex reaction system of the large hydrocarbon molecules of gas–oil.

Highly efficient sorbents for phosphate removal from aqueous solutions based on the calcined forms of Fe(III)-substituted Layered Double Hydroxides (LDH) materials have been developed in this study. Hydrotalcite-like materials with Mg/M(3+) approximately 3 (where M=Al(3+), Fe(3+) or combined) have been synthesized following simple co-precipitation method and were subsequently calcined in air at 450 degrees C. Both as-synthesized and calcined materials were characterized by means of X-ray Diffraction (XRD), Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES), elemental (C) analysis, N(2) porosimetry, Scanning Electron Microscopy (SEM). All the materials were evaluated for the sorption of phosphates by batch equilibrium sorption experiments and kinetic measurements (effect of contact time). It was shown that chlorides or nitrates, being the charge-balancing anions in the LDH structure, are more easily exchanged by phosphates compared to carbonates. In the Fe(III)-modified LDHs, an increase of the Fe loading led to the decrease of the sorption efficiency. The maximum uptake of phosphates for both the Mg-Al LDH and Mg-Fe LDH samples containing mainly carbonates as charge-balancing anions was relatively low (ca.

In this work we synthesized MFI type zeolites with chromium and gallium. Hydrothermal synthesis was applied using, either aluminum with gallium or chromium sources in 1:1 mole ratios, or impregnation of H-ZSM-5 with the desired metal. The “as synthesized” samples were characterized by XRD, Chemical analysis, SEM-EDS, SSA, ammonia-TPD and subjected to severe steaming, in order to suppress their acidity and consequently decrease the oligomerization capability of the formed catalysts. The catalytic activity of the zeolite samples in propane dehydrogenation was investigated using a fixed-bed continuous-flow glass reactor. The catalytic test results revealed that propylene yield and selectivity over the steamed catalysts increased remarkably (e.g. propylene yield 11% with selectivity of 45%, for H-[Ga/Al]ZSM-5), as a consequence of the suppression of their acidity and therefore of the dramatic decrease of their oligomerization capability. The above results suggest that Cr- and Ga-modified steamed zeolites are promising catalysts for the dehydrogenation of propane to propylene.

The present study focuses on the effect of the metal-modification method (ion-exchange or impregnation) and of the type of dealumination procedure (steaming, AHFS) of zeolite-Y on the quantity, quality and properties of the carbon nanotubes that are formed on the supported iron or cobalt oxides. Severe dealumination of zeolite-Y by steaming, which induced secondary meso/macropores, resulted in significant decrease in the carbon nanotube formation activity of the metal-impregnated zeolite-Y catalysts, while moderate dealumination by ammonium hexafluorosilicate had a less pronounced effect. The micro-Raman spectra revealed the presence of high quality as-grown CNTs with low degree of disordered.

The hydrothermally-stable and acidic MSU-S aluminosilicates assembled from zeolite seeds has been shown to be significantly more active in the cracking of gas-oil, compared to an amorphous commercial silica-alumina catalyst, after moderate steaming pretreatment. When compared to a similarly steamed H-Y based catalyst at constant conversion, the MSU-S catalytic material produced less gasoline and more LCO, while it was more selective for the production of propylene and butylenes, as well as of gasoline range alkenes. The differences in catalytic activity and product selectivity were related to differences in the pore structure/size and in the nature/strength of the acid sites of the tested materials. When the MSU-S materials were tested as FCC catalyst additives, at a concentration level of 8 wt.% on total catalyst weight, they induced higher conversion of gas-oil, mainly due to the increase of LPGs, coke and gasoline range aromatics.