Lori Nalbandian | Chemical Process Engineering Research Institure (original) (raw)

Papers by Lori Nalbandian

Thermochimica Acta, 2004

Titania supported vanadia catalysts (2.5, 5, and 11 wt.% V 2 O 5 ) were prepared by a wet impregn... more Titania supported vanadia catalysts (2.5, 5, and 11 wt.% V 2 O 5 ) were prepared by a wet impregnation technique and their thermal behavior, morphology as well as redox properties were examined by thermal analysis methods thermogravimetry (TGA), differential scanning calorimetry (DSC), temperature programmed-evolved gas analysis with mass spectroscopy, (EGA-MS), scanning electron microscopy (SEM), and temperature programmed reduction (TPR). The two Eurocat samples EL10V1 and EL10V8 containing 1 and 8 wt.% V 2 O 5 were also characterized using the same techniques. Thermal decomposition of vanadium oxide precursors (ammonium vanadyl oxalate) supported on TiO 2 as evidenced by thermal analysis, occurs in three successive steps, which are influenced by the surrounding atmosphere (oxidative, reductive, and inert). The presence of tower-like vanadia crystals in the sample with the highest vanadia loading (11 wt.% V 2 O 5 ) was identified by SEM. The H 2 -TPR experiments revealed that the reduction temperature is a factor of the vanadia loading and the type of support. Vanadia species supported on Norton titania are more reducible that those supported on Eurocat titania.

Applied Catalysis A-general, 2007

In this work, we report an in-depth structural characterization of pure NiO and Ni-Nb-O mixed oxi... more In this work, we report an in-depth structural characterization of pure NiO and Ni-Nb-O mixed oxide catalysts (Nb/Ni = 0-0.25), highly active and selective materials for ethylene production via ethane ODH, using high resolution transmission electron microscopy (HRTEM) coupled with energy dispersive X-ray analysis (EDS). This study led to the identification and investigation of the nanostructural features formed in the Nb-doped NiO catalysts and their relation with the excellent catalytic functionality of the Ni-Nb-O materials. It was found that low-temperature treatment of pure NiO leads to the formation of a non-stoichiometric oxidic phase with characteristic structural defects due to cationic deficiency, as demonstrated by microscopy results. On the Nb-doped oxides, two distinct structural phases, formed via the reaction of the Nb cations with the cationic vacancies, were identified: a NiO phase having Nb cations incorporated in the host lattice, which retains its initial cubic structure (Ni-Nb solid solution), and a highly distorted Nb-rich phase, precursor for the formation of the mixed NiNb 2 O 6 crystal compound. The reduction of the structural defects in NiO via their interaction with the niobium ions was correlated with the extremely high selectivity of the Ni-Nb-O catalysts to ethylene in the ethane ODH reaction, since these vacancies lead to the formation of strong oxidizing electrophilic oxygen species (O À ), responsible for the total oxidation of ethane to CO 2 .

Microporous and Mesoporous Materials, 2004

Partially crystalline and X-ray amorphous ZSM-5 zeolite-based aluminosilicates have been synthesi... more Partially crystalline and X-ray amorphous ZSM-5 zeolite-based aluminosilicates have been synthesized and thoroughly characterized by chemical analysis, XRD, FT-IR, solid state MAS NMR, N 2 adsorption, TEM, NH 3 -TPD and isopropanol dehydration as the catalytic test reaction. The X-ray amorphous and low-crystallinity samples were hydrothermally synthesized at temperatures as low as 25°C and consisted of nanosized well-formed particles of almost spherical shape and with dimensions of about 20-30 nm. These samples exhibited very low microporosity and remarkably high meso/macropore volume (pore diameters P30 nm) and/or high external surface area. The first Bragg peaks were observed in the XRD patterns of the samples synthesized at 90°C and their position on the 2h-axis was the same as those of a reference highly crystalline ZSM-5 zeolite sample. The particle/crystal size and microporosity of the partially crystalline materials increased with increasing hydrothermal synthesis temperature and % relative XRD crystallinity. Incorporation of aluminum in the ZSM-5 zeolitic framework was significantly enhanced at higher relative crystallinities, i.e. >60%. The X-ray amorphous aluminosilicates possessed tetrahedral aluminum atoms which were more zeolitic in character and induced a higher number of acidic framework hydroxyls (Brønsted acid sites), as compared to those found in a conventional silica-alumina.

Microporous and Mesoporous Materials, 2008

The effect of the textural properties and morphology of zeolite Y, used as support of iron (Fe) o... more 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.

Vibrational Spectroscopy, 1992

Raman spectra of gold(III) chloride in the solid and vapor (Au2Cl6(g)) phases and of the vapor co... more Raman spectra of gold(III) chloride in the solid and vapor (Au2Cl6(g)) phases and of the vapor complex AuAlC16(g) have been measured at temperatures up to 570 K. The distribution of vibrational modes in AuCl3(s) have been derived and six low frequency Raman bands have been assigned to librational modes of the solid. Fifteen internal modes of the AuCla(s) have been measured in the Raman and IR spectra and were assigned to the AuECl 6 molecule in the crystal. Normal coordinate analysis was performed and a complete force field was derived for the AuECl 6 in the crystal. Experimental difficulties arising from laser induced decomposition of the colored vapors Au2CI 6 and AuAlCl 6 were overcome by using a rotating Raman cell inside the optical furnace. Four polarized bands at 386, 324, 157 and 96 cm-1 and their combinations and overtones have been measured in the resonance Raman spectra of Au2Cl6(g). The Raman intensities of the AuAlC16(g) were also resonance enhanced and seven polarized fundamentals have been measured at 495, 386, 330, 300, 183, 156 and 98 cm 1. A tentative normal coordinate analysis was performed for AuECl6(g) and AuAlC16(g). The force field calculations of AuAICl6(g) with a Cz~, symmetry were based on a procedure of mixing the force constants of the AleCl6(g) and AuECl6(g).

Cheminform, 1992

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was e... more ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Inorganic Chemistry, 1991

conversion rates in the system studied here can be explained by intramolecular phenomena that mig... more conversion rates in the system studied here can be explained by intramolecular phenomena that might result from the intermolecular effects such as packing differences. X-ray crystallographic analyses of both salts at different temperatures showed that the ligand bond length changes in the as "pared to the PF6-salt. We conclude that the activation energy A& for the BPh4-salt is smaller than that for the PF6salt, and this implies the more rapid spin interconversion in the BPh4-salt.

Cheminform, 1992

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was e... more ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Inorganic Chemistry, 1992

Microporous and Mesoporous Materials, 2001

A series of H-ZSM-5 zeolites with dierent framework Si/Al ratios were prepared by hydrothermal sy... more A series of H-ZSM-5 zeolites with dierent framework Si/Al ratios were prepared by hydrothermal synthesis and post-synthesis dealumination by various methods, i.e., HCl, steaming, steaming/HCl and ammonium hexa¯uorosilicate (AHFS). The degree of framework dealumination and the amount/type of the extra-framework phases formed were greatly dependent on the method of dealumination and the severity of the experimental conditions. The hydrothermal treatment of a parent ZSM-5 sample with Si/Al $ 27 was very eective and produced signi®cant amounts of Si±Al extra-framework phases, while the reaction with HCl in relatively strongly acidic environments resulted in very low dealumination. Treatment with AHFS was proven to be an appropriate method for preparing moderately dealuminated H-ZSM-5 samples which are free from extra-framework Al. The relative crystallinity and the microporosity of all dealuminated H-ZSM-5 zeolites were retained to a high degree (>80%), even for the severely steamed samples ($96% dealumination). The morphology of the crystals/particles was not changed signi®cantly; however, each dealumination method had a dierent eect on the partial breakdown of the crystals and on the formation of extra-framework/ amorphous phases with a mesoporous character. The number of acid sites that corresponded to the high-temperature desorption peak of the ammomia-temperature programmed desorption spectra was found to be equivalent to the framework Al (FAl) content of all H-ZSM-5 samples, irrespective of the degree of dealumination and the amount of extra-framework phases. Theses phases had a low capability of adsorbing ammonia compared to the FAl atoms and were the main source of acidity for the severely steamed samples which had almost no FAl. Ó

Catalysis Today, 2000

The oxidative dehydrogenation of propane was investigated using vanadia type catalysts supported ... more The oxidative dehydrogenation of propane was investigated using vanadia type catalysts supported on Al 2 O 3 , TiO 2 , ZrO 2 and MgO. The promotion of V 2 O 5 /Al 2 O 3 catalyst with alkali metals (Li, Na, K) was also attempted. Evaluation of temperature programmed reduction patterns showed that the reducibility of V species is affected by the support acid-base character. The catalytic activity is favored by the V reducibility of the catalyst as it was confirmed from runs conducted at 450-550 • C. V 2 O 5 /TiO 2 catalyst exhibits the highest activity in oxydehydrogenation of propane. The support's nature also affects the selectivity to propene; V 2 O 5 supported on Al 2 O 3 catalyst exhibits the highest selectivity. Reaction studies showed that addition of alkali metals decreases the catalytic activity in the order non-doped>Li>Na>K. Propene selectivity significantly increases in the presence of doped catalysts.

Applied Catalysis A-general, 1993

Industrial & Engineering Chemistry Research, 1999

... Lori Nalbandian and Iakovos A. Vasalos. Chemical Process Engineering Research Institute and D... more ... Lori Nalbandian and Iakovos A. Vasalos. Chemical Process Engineering Research Institute and Department of Chemical Engineering, Aristotelian University of Thessaloniki, PO Box 361, 57001 Thermi, Thessaloniki, Greece. Ind. Eng. Chem. Res. ...

Catalysis Today, 2007

Two commercial FCC catalysts were investigated to explore the effect of their different accessibi... more Two commercial FCC catalysts were investigated to explore the effect of their different accessibility on the catalyst activity, selectivity and deactivation due to deleterious feed metals (V and Ni). Feed metal Fe was not included in the present study. E-Cats (equilibrium samples from a commercial FCC unit) of both FCC catalysts and the corresponding laboratory-deactivated samples (applying the cyclic deactivation

Catalysis Today, 2001

In this work the effects of two metal poisons (Ni, V) on FCC products were investigated in an FCC... more In this work the effects of two metal poisons (Ni, V) on FCC products were investigated in an FCC pilot plant. The most important effects of metals were found on the gasoline, coke and H 2 yields. A comparison study of the metal distribution in the catalyst particles aged in the FCC pilot plant, a CDU and an industrial FCCU was also performed using a SEM-EDS method. SEM results showed that the metal profiles from CDU samples simulate more satisfactorily the profiles of the E-cat than that from the FCC pilot plant.

Applied Catalysis B-environmental, 2005

Ir-based additives, developed to reduce NO and CO emitted during the regeneration of spent fluid ... more Ir-based additives, developed to reduce NO and CO emitted during the regeneration of spent fluid catalytic cracking (FCC) catalysts were characterized to correlate physicochemical properties with catalytic performance. Support, metal loading and the state of the metal significantly affected the catalytic performance. Increasing the Ir loading or using a Ce-promoted γ-alumina (CPBase) support results in the formation of larger Ir particles. Local reduction of iridium oxide surface in such particles leads to coexisting Ir and Ir2O phases being very beneficial for the catalytic activity.NO reduction and CO oxidation take place thermally at 700°C. Increasing the O2 concentration in the feed favors CO oxidation at the expense of NO reduction. With 500ppmIr/CPBase and 1000ppmIr/CPBase additives, complete NO reduction and CO oxidation is achieved in the presence of 40% excess oxygen. Higher oxygen excess, however, reduces or eliminates the NOx reduction activity of these materials. IR studies suggest that NO reduction by CO proceeds on Ir/alumina additives via the dissociative adsorption of NO, the formation of NCO species on Ir and their migration to the alumina support, where N2 and CO2 are formed. IR spectroscopy indicates that Ce modifies the Ir surface enhancing the CO oxidation and enabling NO reduction via the NO2 formation.

Microporous and Mesoporous Materials, 2008

Nanocrystalline particles of Mn x Zn 1Àx Fe 2 O 4 were prepared by chemical precipitation of hydr... more Nanocrystalline particles of Mn x Zn 1Àx Fe 2 O 4 were prepared by chemical precipitation of hydroxides, followed by hydrothermal processing and freeze-drying. The synthesis involves the hydrolysis of aqueous metal precursors by using ammonia as precipitating agent. The chlorine ion concentration in the solution and the pH of the precipitation, are shown to play a crucial role in retaining the initial stoichiometry of the solution to the nanoparticles. The obtained products exhibited some interesting and unique features: they consisted of nanoparticles with sizes ranging from 5 to 25 nm, they had surface areas between 60 and 110 m 2 g À1 and pore sizes in the mesopore region (i.e. 8-20 nm). The produced materials were examined by powder X-ray diffraction for crystalline phase identification, scanning electron microscopy for grain morphology, high resolution transmission electron microscopy for particle size distribution and nitrogen sorption for surface area, pore volume and pore size distribution determination. The sintering of the ferrite powders was also studied by thermogravimetric analysis and dilatometry of the powders mixed with an organic binder to improve their compaction properties.

Journal of Solar Energy Engineering-transactions of The Asme, 2006

A promising method for the conversion and storage of solar energy into hydrogen is the dissociati... more A promising method for the conversion and storage of solar energy into hydrogen is the dissociation of water into oxygen and hydrogen, carried out via a two-step process using metal oxide redox systems such as mixed iron oxides, coated upon multi-channeled honeycomb ceramic supports capable of absorbing solar irradiation, in a configuration similar to that encountered in automobile exhaust catalytic converters. With this configuration, the whole process can be carried out in a single solar energy converter, the process temperature can be significantly lowered compared to other thermo-chemical cycles and the recombination of oxygen and hydrogen is prevented by fixing the oxygen in the metal oxide. For the realization of the integrated concept, research work proceeded in three parallel directions: synthesis of active redox systems, manufacture of ceramic honeycomb supports and manufacture, testing and optimization of operating conditions of a thermochemical solar receiver-reactor. The receiver-reactor has been developed and installed in the solar furnace in Cologne, Germany. It was proven that solar hydrogen production is feasible by this process demonstrating that multicycling of the process was possible in principle.

Journal of The European Ceramic Society, 2007

Journal of Membrane Science, 2008

The redox water splitting is one of the most promising routes for sustainable hydrogen production... more The redox water splitting is one of the most promising routes for sustainable hydrogen production. Towards this goal, serious technological obstacles are set: (i) by the non-isothermal operation of the redox process, that causes serious reactor construction problems, and (ii) by the need for efficient high temperature oxygen/hydrogen separation technology which is a very challenging development. In this paper, perovskite materials having the formula La 0.3 Sr 0.7 FeO 3 were synthesized and subsequently tested for their high temperature oxidation/reduction behavior. The redox activity of the materials in relation to the water splitting reaction has been also investigated. Dense, disc shaped membranes of the materials were synthesized and placed in a membrane reactor. Experiments at 1133 K revealed the possibility of performing the reduction and oxidation steps simultaneously and isothermally on each side of the membrane reactor. A steady-state situation was thereby achieved where hydrogen was continuously produced on one side while the material was simultaneously regenerated on the other side. The created oxygen vacancy gradient formed the driving force for a continuous flux of vacancies from the membrane reduction surface to the membrane oxidation surface. The hydrogen production rate under the particular experimental conditions estimated to be ∼47.5 cm 3 H 2 (STP) m −2 min −1 . It could be increased by a factor of approximately 3, up to ∼145 cm 3 H 2 (STP) m −2 min −1 , if the membrane reduction was enhanced with a reductant such as carbon monoxide. This approach resulted in an efficient execution of the water gas shift reaction towards high purity hydrogen production.

Thermochimica Acta, 2004

Titania supported vanadia catalysts (2.5, 5, and 11 wt.% V 2 O 5 ) were prepared by a wet impregn... more Titania supported vanadia catalysts (2.5, 5, and 11 wt.% V 2 O 5 ) were prepared by a wet impregnation technique and their thermal behavior, morphology as well as redox properties were examined by thermal analysis methods thermogravimetry (TGA), differential scanning calorimetry (DSC), temperature programmed-evolved gas analysis with mass spectroscopy, (EGA-MS), scanning electron microscopy (SEM), and temperature programmed reduction (TPR). The two Eurocat samples EL10V1 and EL10V8 containing 1 and 8 wt.% V 2 O 5 were also characterized using the same techniques. Thermal decomposition of vanadium oxide precursors (ammonium vanadyl oxalate) supported on TiO 2 as evidenced by thermal analysis, occurs in three successive steps, which are influenced by the surrounding atmosphere (oxidative, reductive, and inert). The presence of tower-like vanadia crystals in the sample with the highest vanadia loading (11 wt.% V 2 O 5 ) was identified by SEM. The H 2 -TPR experiments revealed that the reduction temperature is a factor of the vanadia loading and the type of support. Vanadia species supported on Norton titania are more reducible that those supported on Eurocat titania.

Applied Catalysis A-general, 2007

In this work, we report an in-depth structural characterization of pure NiO and Ni-Nb-O mixed oxi... more In this work, we report an in-depth structural characterization of pure NiO and Ni-Nb-O mixed oxide catalysts (Nb/Ni = 0-0.25), highly active and selective materials for ethylene production via ethane ODH, using high resolution transmission electron microscopy (HRTEM) coupled with energy dispersive X-ray analysis (EDS). This study led to the identification and investigation of the nanostructural features formed in the Nb-doped NiO catalysts and their relation with the excellent catalytic functionality of the Ni-Nb-O materials. It was found that low-temperature treatment of pure NiO leads to the formation of a non-stoichiometric oxidic phase with characteristic structural defects due to cationic deficiency, as demonstrated by microscopy results. On the Nb-doped oxides, two distinct structural phases, formed via the reaction of the Nb cations with the cationic vacancies, were identified: a NiO phase having Nb cations incorporated in the host lattice, which retains its initial cubic structure (Ni-Nb solid solution), and a highly distorted Nb-rich phase, precursor for the formation of the mixed NiNb 2 O 6 crystal compound. The reduction of the structural defects in NiO via their interaction with the niobium ions was correlated with the extremely high selectivity of the Ni-Nb-O catalysts to ethylene in the ethane ODH reaction, since these vacancies lead to the formation of strong oxidizing electrophilic oxygen species (O À ), responsible for the total oxidation of ethane to CO 2 .

Microporous and Mesoporous Materials, 2004

Partially crystalline and X-ray amorphous ZSM-5 zeolite-based aluminosilicates have been synthesi... more Partially crystalline and X-ray amorphous ZSM-5 zeolite-based aluminosilicates have been synthesized and thoroughly characterized by chemical analysis, XRD, FT-IR, solid state MAS NMR, N 2 adsorption, TEM, NH 3 -TPD and isopropanol dehydration as the catalytic test reaction. The X-ray amorphous and low-crystallinity samples were hydrothermally synthesized at temperatures as low as 25°C and consisted of nanosized well-formed particles of almost spherical shape and with dimensions of about 20-30 nm. These samples exhibited very low microporosity and remarkably high meso/macropore volume (pore diameters P30 nm) and/or high external surface area. The first Bragg peaks were observed in the XRD patterns of the samples synthesized at 90°C and their position on the 2h-axis was the same as those of a reference highly crystalline ZSM-5 zeolite sample. The particle/crystal size and microporosity of the partially crystalline materials increased with increasing hydrothermal synthesis temperature and % relative XRD crystallinity. Incorporation of aluminum in the ZSM-5 zeolitic framework was significantly enhanced at higher relative crystallinities, i.e. >60%. The X-ray amorphous aluminosilicates possessed tetrahedral aluminum atoms which were more zeolitic in character and induced a higher number of acidic framework hydroxyls (Brønsted acid sites), as compared to those found in a conventional silica-alumina.

Microporous and Mesoporous Materials, 2008

The effect of the textural properties and morphology of zeolite Y, used as support of iron (Fe) o... more 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.

Vibrational Spectroscopy, 1992

Raman spectra of gold(III) chloride in the solid and vapor (Au2Cl6(g)) phases and of the vapor co... more Raman spectra of gold(III) chloride in the solid and vapor (Au2Cl6(g)) phases and of the vapor complex AuAlC16(g) have been measured at temperatures up to 570 K. The distribution of vibrational modes in AuCl3(s) have been derived and six low frequency Raman bands have been assigned to librational modes of the solid. Fifteen internal modes of the AuCla(s) have been measured in the Raman and IR spectra and were assigned to the AuECl 6 molecule in the crystal. Normal coordinate analysis was performed and a complete force field was derived for the AuECl 6 in the crystal. Experimental difficulties arising from laser induced decomposition of the colored vapors Au2CI 6 and AuAlCl 6 were overcome by using a rotating Raman cell inside the optical furnace. Four polarized bands at 386, 324, 157 and 96 cm-1 and their combinations and overtones have been measured in the resonance Raman spectra of Au2Cl6(g). The Raman intensities of the AuAlC16(g) were also resonance enhanced and seven polarized fundamentals have been measured at 495, 386, 330, 300, 183, 156 and 98 cm 1. A tentative normal coordinate analysis was performed for AuECl6(g) and AuAlC16(g). The force field calculations of AuAICl6(g) with a Cz~, symmetry were based on a procedure of mixing the force constants of the AleCl6(g) and AuECl6(g).

Cheminform, 1992

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was e... more ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Inorganic Chemistry, 1991

conversion rates in the system studied here can be explained by intramolecular phenomena that mig... more conversion rates in the system studied here can be explained by intramolecular phenomena that might result from the intermolecular effects such as packing differences. X-ray crystallographic analyses of both salts at different temperatures showed that the ligand bond length changes in the as "pared to the PF6-salt. We conclude that the activation energy A& for the BPh4-salt is smaller than that for the PF6salt, and this implies the more rapid spin interconversion in the BPh4-salt.

Cheminform, 1992

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was e... more ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Inorganic Chemistry, 1992

Microporous and Mesoporous Materials, 2001

A series of H-ZSM-5 zeolites with dierent framework Si/Al ratios were prepared by hydrothermal sy... more A series of H-ZSM-5 zeolites with dierent framework Si/Al ratios were prepared by hydrothermal synthesis and post-synthesis dealumination by various methods, i.e., HCl, steaming, steaming/HCl and ammonium hexa¯uorosilicate (AHFS). The degree of framework dealumination and the amount/type of the extra-framework phases formed were greatly dependent on the method of dealumination and the severity of the experimental conditions. The hydrothermal treatment of a parent ZSM-5 sample with Si/Al $ 27 was very eective and produced signi®cant amounts of Si±Al extra-framework phases, while the reaction with HCl in relatively strongly acidic environments resulted in very low dealumination. Treatment with AHFS was proven to be an appropriate method for preparing moderately dealuminated H-ZSM-5 samples which are free from extra-framework Al. The relative crystallinity and the microporosity of all dealuminated H-ZSM-5 zeolites were retained to a high degree (>80%), even for the severely steamed samples ($96% dealumination). The morphology of the crystals/particles was not changed signi®cantly; however, each dealumination method had a dierent eect on the partial breakdown of the crystals and on the formation of extra-framework/ amorphous phases with a mesoporous character. The number of acid sites that corresponded to the high-temperature desorption peak of the ammomia-temperature programmed desorption spectra was found to be equivalent to the framework Al (FAl) content of all H-ZSM-5 samples, irrespective of the degree of dealumination and the amount of extra-framework phases. Theses phases had a low capability of adsorbing ammonia compared to the FAl atoms and were the main source of acidity for the severely steamed samples which had almost no FAl. Ó

Catalysis Today, 2000

The oxidative dehydrogenation of propane was investigated using vanadia type catalysts supported ... more The oxidative dehydrogenation of propane was investigated using vanadia type catalysts supported on Al 2 O 3 , TiO 2 , ZrO 2 and MgO. The promotion of V 2 O 5 /Al 2 O 3 catalyst with alkali metals (Li, Na, K) was also attempted. Evaluation of temperature programmed reduction patterns showed that the reducibility of V species is affected by the support acid-base character. The catalytic activity is favored by the V reducibility of the catalyst as it was confirmed from runs conducted at 450-550 • C. V 2 O 5 /TiO 2 catalyst exhibits the highest activity in oxydehydrogenation of propane. The support's nature also affects the selectivity to propene; V 2 O 5 supported on Al 2 O 3 catalyst exhibits the highest selectivity. Reaction studies showed that addition of alkali metals decreases the catalytic activity in the order non-doped>Li>Na>K. Propene selectivity significantly increases in the presence of doped catalysts.

Applied Catalysis A-general, 1993

Industrial & Engineering Chemistry Research, 1999

... Lori Nalbandian and Iakovos A. Vasalos. Chemical Process Engineering Research Institute and D... more ... Lori Nalbandian and Iakovos A. Vasalos. Chemical Process Engineering Research Institute and Department of Chemical Engineering, Aristotelian University of Thessaloniki, PO Box 361, 57001 Thermi, Thessaloniki, Greece. Ind. Eng. Chem. Res. ...

Catalysis Today, 2007

Two commercial FCC catalysts were investigated to explore the effect of their different accessibi... more Two commercial FCC catalysts were investigated to explore the effect of their different accessibility on the catalyst activity, selectivity and deactivation due to deleterious feed metals (V and Ni). Feed metal Fe was not included in the present study. E-Cats (equilibrium samples from a commercial FCC unit) of both FCC catalysts and the corresponding laboratory-deactivated samples (applying the cyclic deactivation

Catalysis Today, 2001

In this work the effects of two metal poisons (Ni, V) on FCC products were investigated in an FCC... more In this work the effects of two metal poisons (Ni, V) on FCC products were investigated in an FCC pilot plant. The most important effects of metals were found on the gasoline, coke and H 2 yields. A comparison study of the metal distribution in the catalyst particles aged in the FCC pilot plant, a CDU and an industrial FCCU was also performed using a SEM-EDS method. SEM results showed that the metal profiles from CDU samples simulate more satisfactorily the profiles of the E-cat than that from the FCC pilot plant.

Applied Catalysis B-environmental, 2005

Ir-based additives, developed to reduce NO and CO emitted during the regeneration of spent fluid ... more Ir-based additives, developed to reduce NO and CO emitted during the regeneration of spent fluid catalytic cracking (FCC) catalysts were characterized to correlate physicochemical properties with catalytic performance. Support, metal loading and the state of the metal significantly affected the catalytic performance. Increasing the Ir loading or using a Ce-promoted γ-alumina (CPBase) support results in the formation of larger Ir particles. Local reduction of iridium oxide surface in such particles leads to coexisting Ir and Ir2O phases being very beneficial for the catalytic activity.NO reduction and CO oxidation take place thermally at 700°C. Increasing the O2 concentration in the feed favors CO oxidation at the expense of NO reduction. With 500ppmIr/CPBase and 1000ppmIr/CPBase additives, complete NO reduction and CO oxidation is achieved in the presence of 40% excess oxygen. Higher oxygen excess, however, reduces or eliminates the NOx reduction activity of these materials. IR studies suggest that NO reduction by CO proceeds on Ir/alumina additives via the dissociative adsorption of NO, the formation of NCO species on Ir and their migration to the alumina support, where N2 and CO2 are formed. IR spectroscopy indicates that Ce modifies the Ir surface enhancing the CO oxidation and enabling NO reduction via the NO2 formation.

Microporous and Mesoporous Materials, 2008

Nanocrystalline particles of Mn x Zn 1Àx Fe 2 O 4 were prepared by chemical precipitation of hydr... more Nanocrystalline particles of Mn x Zn 1Àx Fe 2 O 4 were prepared by chemical precipitation of hydroxides, followed by hydrothermal processing and freeze-drying. The synthesis involves the hydrolysis of aqueous metal precursors by using ammonia as precipitating agent. The chlorine ion concentration in the solution and the pH of the precipitation, are shown to play a crucial role in retaining the initial stoichiometry of the solution to the nanoparticles. The obtained products exhibited some interesting and unique features: they consisted of nanoparticles with sizes ranging from 5 to 25 nm, they had surface areas between 60 and 110 m 2 g À1 and pore sizes in the mesopore region (i.e. 8-20 nm). The produced materials were examined by powder X-ray diffraction for crystalline phase identification, scanning electron microscopy for grain morphology, high resolution transmission electron microscopy for particle size distribution and nitrogen sorption for surface area, pore volume and pore size distribution determination. The sintering of the ferrite powders was also studied by thermogravimetric analysis and dilatometry of the powders mixed with an organic binder to improve their compaction properties.

Journal of Solar Energy Engineering-transactions of The Asme, 2006

A promising method for the conversion and storage of solar energy into hydrogen is the dissociati... more A promising method for the conversion and storage of solar energy into hydrogen is the dissociation of water into oxygen and hydrogen, carried out via a two-step process using metal oxide redox systems such as mixed iron oxides, coated upon multi-channeled honeycomb ceramic supports capable of absorbing solar irradiation, in a configuration similar to that encountered in automobile exhaust catalytic converters. With this configuration, the whole process can be carried out in a single solar energy converter, the process temperature can be significantly lowered compared to other thermo-chemical cycles and the recombination of oxygen and hydrogen is prevented by fixing the oxygen in the metal oxide. For the realization of the integrated concept, research work proceeded in three parallel directions: synthesis of active redox systems, manufacture of ceramic honeycomb supports and manufacture, testing and optimization of operating conditions of a thermochemical solar receiver-reactor. The receiver-reactor has been developed and installed in the solar furnace in Cologne, Germany. It was proven that solar hydrogen production is feasible by this process demonstrating that multicycling of the process was possible in principle.

Journal of The European Ceramic Society, 2007

Journal of Membrane Science, 2008

The redox water splitting is one of the most promising routes for sustainable hydrogen production... more The redox water splitting is one of the most promising routes for sustainable hydrogen production. Towards this goal, serious technological obstacles are set: (i) by the non-isothermal operation of the redox process, that causes serious reactor construction problems, and (ii) by the need for efficient high temperature oxygen/hydrogen separation technology which is a very challenging development. In this paper, perovskite materials having the formula La 0.3 Sr 0.7 FeO 3 were synthesized and subsequently tested for their high temperature oxidation/reduction behavior. The redox activity of the materials in relation to the water splitting reaction has been also investigated. Dense, disc shaped membranes of the materials were synthesized and placed in a membrane reactor. Experiments at 1133 K revealed the possibility of performing the reduction and oxidation steps simultaneously and isothermally on each side of the membrane reactor. A steady-state situation was thereby achieved where hydrogen was continuously produced on one side while the material was simultaneously regenerated on the other side. The created oxygen vacancy gradient formed the driving force for a continuous flux of vacancies from the membrane reduction surface to the membrane oxidation surface. The hydrogen production rate under the particular experimental conditions estimated to be ∼47.5 cm 3 H 2 (STP) m −2 min −1 . It could be increased by a factor of approximately 3, up to ∼145 cm 3 H 2 (STP) m −2 min −1 , if the membrane reduction was enhanced with a reductant such as carbon monoxide. This approach resulted in an efficient execution of the water gas shift reaction towards high purity hydrogen production.