Studies of chemical, thermal stability and durability of catalytic converters based on electropositively promoted Pt.

Η παρούσα Διδακτορική Διατριβή περιλαμβάνει συστηματική μελέτη για την ανάπτυξη τριοδικού καταλυτικού μετατροπέα (TWC) που να επιδεικνύει εξαιρετικές καταλυτικές αποδόσεις και ικανοποιητική θερμική σταθερότητα σε συνδυασμό με μικρό οικονομικό κόστος. Ο τριοδικός καταλυτικός μετατροπέας που παρασκευάζεται αποτελείται από ένα μόνο ευγενές μέταλλο (Pt) σε χαμηλή φόρτιση (0.5 % κ.β.) υποστηριγμένο σε φορέα γ-αλούμινας. Στα τρία κεφάλαια της Διδακτορικής Διατριβής εξετάζονται διάφοροι παράμετροι με στόχο την ενίσχυση του τριοδικού καταλυτικού μετατροπέα έτσι ώστε να καταστεί ανταγωνιστικός των αντίστοιχων εμπορικών. Για την παρασκευή ενός τέτοιου συστήματος στο πρώτο κεφάλαιο διερευνάται η βέλτιστη μεθοδολογία σύνθεσης που να οδηγεί σε υλικό υψηλής ενεργότητας και θερμικής αντοχής. Η σύνθεση της καταλυτικής επίστρωσης που επιλέγεται είναι: 0.5 % Pt ως καταλυτικά ενεργή φάση και μεικτός φορέας αποτελούμενος από 80 % γ-Al2O3 ως κύριο υποστηρικτικό υλικό ενισχυμένο με το στερεό διάλυμα των οξειδίων προωθητών (οξείδια δημητρίου, ζιρκονίου και λανθανίου) κατά 20 %. Εξετάζονται τρεις διαφορετικές μέθοδοι σύνθεσης: αυτές της ταυτόχρονης συγκαταβύθισης, της διαδοχικής συγκαταβύθισης και του υγρού εμποτισμού, καθώς και διαφορετικές πρώτες ύλες τόσο της γ-αλούμινας όσο και των οξειδίων προωθητών. Μετά την παρασκευή των διαφορετικών καταλυτικών φορέων ακολουθεί η επίστρωσή τους μέσω εμβάπτισης σε κορδιεριτικά μονολιθικά υποστρώματα για την ανάκτηση των καταλυτικών αποδόσεων κάτω από συνθήκες προσομοίωσης των καυσαερίων στο στοιχειομετρικό σημείο. Προκειμένου να διερευνηθεί η θερμική σταθερότητα των παραχθέντων υλικών λαμβάνουν χώρα δύο θερμικές κατεργασίες: στους 600 oC για 2 ώρες και στους 900 oC για 5 ώρες παρουσία στατικού αέρα. Ακολουθεί ενδελεχής μελέτη με τη βοήθεια των τεχνικών περίθλασης ακτίνων – Χ (XRD), φυσικής ρόφησης αζώτου Ν2, ηλεκτρονικής μικροσκοπίας σάρωσης (SEM) και ηλεκτρονικής μικροσκοπίας διερχόμενης δέσμης (TEM), με στόχο τον διεξοδικό χαρακτηρισμό των διαφορετικών καταλυτικών δειγμάτων και την συσχέτιση της καταλυτικής τους ενεργότητας με τις φυσικοχημικές τους ιδιότητες. Σύμφωνα με τα αποτελέσματα, το πιο καταλυτικά ενεργό υλικό ακόμα και μετά από θερμική γήρανση στους 900 oC παρασκευάζεται με τη μέθοδο της ταυτόχρονης συγκαταβύθισης. Η ανωτερότητα της μεθόδου αυτής αποδίδεται στη δημιουργία ομοιογενούς υλικού, με το στερεό διάλυμα των οξειδίων προωθητών να εμφανίζεται υψηλά διασπαρμένο στην επιφάνεια της γ-αλούμινας εξασφαλίζοντας μεγαλύτερο αριθμό διεπιφανειών μεταξύ ευγενούς μετάλλου – οξειδίων προωθητών που συντελούν στην αποφυγή φαινομένων συσσωμάτωσης του ευγενούς μετάλλου καθώς και στην αύξηση των καταλυτικά ενεργών κέντρων. Επιπλέον, αποδεικνύεται ότι η χρήση των δύο διαφορετικών πρόδρομων ενώσεων του δημητρίου δεν επιφέρει σημαντικές αλλαγές ούτε στα δομικά – μορφολογικά χαρακτηριστικά του φορέα αλλά ούτε και στις καταλυτικές ιδιότητες. Και στις δύο περιπτώσεις παρατηρείται διατήρηση της κυβικής συμμετρίας του στερεού διαλύματος Ce0.4Zr0.5La0.1O1.95 με αύξηση της θερμοκρασίας. Το γεγονός αυτό αποδίδεται στη παρουσία των σωματιδίων της γ-αλούμινας που λειτουργούν ως εμπόδια διάχυσης και αποτρέπουν τα ανεπιθύμητα φαινόμενα συσσωμάτωσης του στερεού διαλύματος των οξειδίων προωθητών όπως είναι η μεγέθυνση κρυσταλλιτών με επακόλουθο να αποτρέπεται και ο ανεπιθύμητος διαχωρισμός φάσης του στερεού διαλύματος. Στο δεύτερο κεφάλαιο εξετάζεται η επίδραση της χημικής σύστασης του καταλυτικού φορέα στην επίτευξη υψηλών αποδόσεων και στη διατήρηση της θερμικής σταθερότητας του υλικού. Αρχικά αποδεικνύεται η ευεργετική δράση του μεικτού φορέα με παρασκευή και σύγκριση των ακόλουθων φορέων: καθαρής γ-αλούμινας, στερεού διαλύματος οξειδίων Ce0.4Zr0.5La0.1O1.95 και φορέα 80 % γ-Al2O3 με 20 % Ce0.4Zr0.5La0.1O1.95, ως προς τα δομικά και μορφολογικά χαρακτηριστικά τους σε διαφορετικές θερμοκρασίες κατεργασίας. Εν συνεχεία παρασκευάζεται μία σειρά καταλυτικών δειγμάτων μεικτού φορέα διαφορετικής σύνθεσης με την μέθοδο της ταυτόχρονης συγκαταβύθισης προκειμένου να επιλεχθεί ο καταλληλότερος συνδυασμός και η αναλογία των οξειδίων προωθητών (CexZryLazOδ). Τα παραχθέντα υλικά υπόκεινται και πάλι σε δύο θερμικές κατεργασίες 600 oC και 900 oC, για 2 και 5 ώρες αντίστοιχα παρουσία στατικού ατμοσφαιρικού αέρα. Για την ερμηνεία της τριοδικής καταλυτικής συμπεριφοράς πραγματοποιείται εκτενής ανάλυση των φυσικοχημικών ιδιοτήτων των δειγμάτων με τις τεχνικές της διαφορικής θερμικής ανάλυσης (DTA), περίθλασης ακτίνων – Χ (XRD), φυσικής ρόφησης αζώτου Ν2, καθώς και με τη χρήση της θερμοβαρυμετρικής μεθόδου (TG) για τον προσδιορισμό της ικανότητας αποθήκευσης και απελευθέρωσης οξυγόνου (OSC). Με βάση τα αποτελέσματα που προέκυψαν, αποδεικνύεται πως το δείγμα που έχει τροποποιηθεί με το στερεό διάλυμα Ce0.4Zr0.5La0.1O1.95 επιδεικνύει την ανώτερη καταλυτική ενεργότητα κυρίως όσον αφορά στην μετατροπή των οξειδίων του αζώτου, NOx, και μετά τις δύο θερμικές κατεργασίες. Η συμπεριφορά αυτή αποδίδεται κυρίως στην προώθηση της οξειδοαναγωγικής ικανότητας του CeO2 με την προσθήκη Zr4+ και εν μέρει στη θετική δράση του La3+ που συνίσταται στην εισαγωγή επιπλέον επιφανειακών κενών θέσεων οξυγόνου και στον έντονα βασικό του χαρακτήρα. Αντίθετα, η αύξηση του αριθμού των διεπιφανειών ευγενούς μετάλλου – οξειδίων CeO2 που προκύπτει από την προώθηση της διασποράς του ευγενούς μετάλλου αποδεικνύεται παράμετρος μικρότερης σημασίας. Τέλος, η επίδραση του είδους των οξειδίων προωθητών στα μορφολογικά και δομικά χαρακτηριστικά του καταλυτικού φορέα αποκαλύπτεται μετά από θερμική κατεργασία σε υψηλή θερμοκρασία (άνω των 1000 oC), με την ενσωμάτωση των κατιόντων Zr4+ να συντελούν κυρίως στην σταθεροποίηση του οξειδίου του δημητρίου ενώ εκείνη των κατιόντων La3+ να συνεισφέρει στην θερμική ενίσχυση του φορέα της γ-αλούμινας. Στο τρίτο και τελευταίο κεφάλαιο, ως τελική προσπάθεια ενίσχυσης των καταλυτικών ιδιοτήτων του μονομεταλλικού τριοδικού καταλυτικού μετατροπέα εξετάζεται η προσθήκη ηλεκτροθετικών προωθητών, όπως είναι τα αλκάλια. Ως ηλεκτροθετικός προωθητής χρησιμοποιείται το νάτριο, που προστίθεται σε δύο καταλυτικά συστήματα διαφορετικής σύστασης. Συγκεκριμένα, παρασκευάζονται δείγματα με διαφορετική φόρτιση σε ηλεκτροθετική ενίσχυση με στόχο την διερεύνηση της επίδρασης της περιεκτικότητας σε αλκάλιο στην απόδοση του TWC, καθώς και ένα καταλυτικό σύστημα αναφοράς χωρίς την προσθήκη στερεού διαλύματος των οξειδίων προωθητών. Τα ηλεκτροθετικά ενισχυμένα συστήματα μελετώνται ως προς τα δομικά, μορφολογικά χαρακτηριστικά μετά από δυο θερμικές κατεργασίες στους 600 oC και 900 oC και συσχετίζονται με την καταλυτική ενεργότητα. Όπως αποδεικνύεται, οι φάσεις με τις οποίες εμφανίζεται ο ηλεκτροθετικός προωθητής στους 600 οC είναι τα νιτρικά και νιτρώδη άλατα τα οποία στην αυξημένη θερμοκρασία των 900 oC αποσυντίθενται προς σχηματισμό των φάσεων β/β΄΄ -αλούμινας. Όσον αφορά στην καταλυτική συμπεριφορά, η ηλεκτροθετική ενίσχυση συντελεί στην δημιουργία εξαιρετικά ενεργού καταλυτικού συστήματος με αποδόσεις ανώτερες και από εκείνες εμπορικού διμεταλλικού καταλύτη (Pt/Rh) με 4.5 φορές υψηλότερη φόρτιση σε ευγενές μέταλλο. Συγκεκριμένα, το καταλυτικό σύστημα με την υψηλότερη φόρτιση σε αλκάλιο εμφανίζει θεαματική θερμική σταθερότητα μετά από θερμική γήρανση στους 900 oC με διατήρηση των τιμών μετατροπής των ρύπων κοντά στο 100 %. Η ενίσχυση της καταλυτικής ενεργότητας των δειγμάτων με τη προσθήκη του αλκαλίου αποδίδεται στη μεταβολή των δεσμών χημειορόφησης των αντιδρώντων μορίων με τη μεταλλική επιφάνεια. Η ενσωμάτωση του αλκαλίου στο φορέα της αλούμινας προς σχηματισμό των φάσεων β/β΄΄-αλούμινας αποδεικνύεται κύρια αιτία για την αυξημένη θερμική σταθερότητα καθώς με τον τρόπο αυτό διασφαλίζεται η στενή επαφή και άρα η διατήρηση των ηλεκτρονιακών αλληλεπιδράσεων μεταξύ του ευγενούς μετάλλου και του αλκαλίου. Τέλος, ιδιαίτερα ενθαρρυντικό αποτέλεσμα αποτελεί η μη εξάρτιση των καταλυτικών αποδόσεων από τα μορφολογικά χαρακτηριστικά του φορέα, αφού έντονα υποβαθμισμένη πορώδης δομή και πολύ μικρές τιμές ειδικής επιφάνειας συνδυάζονται με θεαματικές αποδόσεις. Το γεγονός αυτό καθιστά τα ηλεκτροθετικά ενισχυμένα δείγματα πολλά υποσχόμενα υλικά στο χώρο της αυτοκινητοβιομηχανίας αφού η μείωση της ειδικής επιφάνειας θεωρείται ένας από τους βασικότερους παράγοντες θερμικής απενεργοποίησης των τριοδικών καταλυτικών μετατροπέων.The present study involves a thorough investigation on the development of a highly active, thermally stable and cost-effective three–way catalytic converter (TWC). The aim of this work was to enhance physicochemical and catalytic properties of a monometallic Pt/γ-Al2O3 TWC with very low noble metal loading (0.5 % wt.) so as to yield it competitive against commercial TWCs. This was realized by employing an adequate synthesis route, a composite and highly active supporting material and additives such as electropositive promoters. As a start, a composite TWC washcoat consisting of 80 wt % of γ-alumina as the main supporting material promoted with 20 wt % of ceria based solid solution was prepared and the effect of different synthesis routes was investigated. More precisely two coprecipitation methods: simultaneous and sequential; and the impregnation method employing two different γ-alumina powders: one commercial γ-alumina nanopowder and one produced from precipitation of aluminium nitrate were examined. Furthermore simultaneous coprecipitation was studied by using two different cerium precursors: cerium (III) nitrate and ammonium cerium (IV) nitrate. One precious metal, Pt, at low loading (0.5 wt %) was added to the above washcoat materials through a wet–impregnation technique. The as produced catalysts were loaded on cordierite monoliths (TWCs form) via dip coating so as to acquire catalytic activity measurements under simulated exhaust conditions at the stoichiometric point. Physicochemical and catalytic properties of the washcoats were examined after calcination at 600 oC for 2 h and thermal aging at 900 oC for 5 h in air. X-ray diffraction (XRD), Brunauer–Emmett–Teller physical adsorption (BET) scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were applied for the correlation of the samples’ catalytic behavior with their microstructure and morphological characteristics. Among the synthesis routes examined simultaneous coprecipitation yielded materials with superior structural and thermal stability, and catalytic activity properties. TWCs prepared through this route exhibit the optimum catalytic performance, after both thermal treatments, providing the maximum NO, CO and C3H6 conversions and the lowest light-off temperatures. The key factor for this optimum behavior is the higher degree of washcoat homogeneity which inhibits Pt sintering, thus leading to increased noble metal–solid solution interfacial sites. The use of different cerium precursor materials did not have a strong impact on washcoat structural properties or on catalytic performance upon thermal aging. In fact, in both cases no phase segregation of ceria based solid solution was observed in the entire temperature range investigated. This behavior is attributed to the presence of alumina in the washcoat which acts as a diffusion barrier inhibiting solid solution grain growth that could lead to the undesirable phase segregation. Over a second stage, a systematic study was carried out in order to elucidate the influence of different oxide promoters on catalytic activity and thermal durability as well as to correlate important physicochemical properties of promoted catalysts with their three–way catalytic performance. For this purpose, catalytic powders with different ceria based solid solutions, CexZryLazOδ, were produced and properties such as microstructure, pore structure characteristics, oxygen storage capacity and noble metal dispersion in the fresh state and upon thermal aging at 900 oC in an oxidative atmosphere were evaluated. Further, cordierite monoliths were coated with the as developed powders in order to attain catalytic activity measurements under simulated exhaust conditions at the stoichiometric point. It was found that doping ceria with Zr4+ and/or La3+ cations leads to enhanced catalytic performance at the fresh state and significant stability after thermal aging. The highest activity especially in NO conversion and thermal durability was demonstrated by Pt/ACZL catalyst containing Ce0.4Zr0.5La0.1O1.95 solid solution. Correlation of the catalytic performance with physicochemical properties of the examined catalytic samples revealed that enhanced reducibility of ceria based solid solution was a much more essential parameter than the number of metal-support interfacial sites originating from the increased noble metal dispersion. Great differences among the as developed samples in terms of structural and morphological characteristics were displayed by elevating the calcination temperature at 1100 oC demonstrating the beneficial effect of mainly Zr doping on ceria’s stabilization and of La doping on alumina’s stabilization. After concluding on the optimum synthesis procedure and washcoat composition, a final effort to improve the catalytic behavior of the monometallic TWC involved alkali addition. For this reason, catalytic samples consisting of γ-alumina supports modified by two ceria based solid solutions and sodium serving as electropositive promoter, were prepared. In order to evaluate thermal durability, samples were subjected to heat treatment at the elevated temperature of 900 oC in an oxidative atmosphere and activity measurements were acquired. Catalysts with different sodium content were produced together with a reference sample with no oxide modifiers, in order to consider several issues such as optimal alkali loading, location of electropositive promoter before and after thermal treatment at an elevated temperature, synergetic effect between alkali promoter and rare earth modifiers, and finally the potential practical application of the as developed catalytic samples by comparing them with a commercial bimetallic Pt/Rh TWC with significantly higher noble metal loading. An extensive structural and textural investigation (TG/DTA, XRD, N2 adsorption, SEM, TEM analyses) was performed and correlated with catalytic activity. Electrochemical promotion resulted in remarkable improvement of catalytic properties at the fresh state along with extraordinary thermal stability. The pronounced effect of alkali addition was further elucidated by comparing the as prepared catalytic samples to the commercial bimetallic TWC. As revealed, the sample with the maximum alkali content (15 % wt) exhibited ~100 % conversion of all pollutants even after aging, whereas the activity of the commercial TWC varied between 63 – 85 %. The principal effect of sodium at the fresh state is mainly attributed to the modification of noble metal’s chemisorptive properties; whereas the remarkable thermal durability can be rationalized via the in situ formation of a solid electrolyte (β΄΄-alumina) which can act as Na+ ion conductor and therefore modify the surface and catalytic properties of metal sites interfaced with the β΄΄-alumina crystals. Finally, a very promising feature of these materials proved to be the independence of the catalytic behavior with respect to surface area, since degradation of textural characteristics is one of the major causes of TWCs deactivation.The present study involves a thorough investigation on the development of a highly active, thermally stable and cost-effective three–way catalytic converter (TWC). The aim of this work was to enhance physicochemical and catalytic properties of a monometallic Pt/γ-Al2O3 TWC with very low noble metal loading (0.5 % wt.) so as to yield it competitive against commercial TWCs. This was realized by employing an adequate synthesis route, a composite and highly active supporting material and additives such as electropositive promoters. As a start, a composite TWC washcoat consisting of 80 wt % of γ-alumina as the main supporting material promoted with 20 wt % of ceria based solid solution was prepared and the effect of different synthesis routes was investigated. More precisely two coprecipitation methods: simultaneous and sequential; and the impregnation method employing two different γ-alumina powders: one commercial γ-alumina nanopowder and one produced from precipitation of aluminium nitrate were examined. Furthermore simultaneous coprecipitation was studied by using two different cerium precursors: cerium (III) nitrate and ammonium cerium (IV) nitrate. One precious metal, Pt, at low loading (0.5 wt %) was added to the above washcoat materials through a wet–impregnation technique. The as produced catalysts were loaded on cordierite monoliths (TWCs form) via dip coating so as to acquire catalytic activity measurements under simulated exhaust conditions at the stoichiometric point. Physicochemical and catalytic properties of the washcoats were examined after calcination at 600 oC for 2 h and thermal aging at 900 oC for 5 h in air. X-ray diffraction (XRD), Brunauer–Emmett–Teller physical adsorption (BET) scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were applied for the correlation of the samples’ catalytic behavior with their microstructure and morphological characteristics. Among the synthesis routes examined simultaneous coprecipitation yielded materials with superior structural and thermal stability, and catalytic activity properties. TWCs prepared through this route exhibit the optimum catalytic performance, after both thermal treatments, providing the maximum NO, CO and C3H6 conversions and the lowest light-off temperatures. The key factor for this optimum behavior is the higher degree of washcoat homogeneity which inhibits Pt sintering, thus leading to increased noble metal–solid solution interfacial sites. The use of different cerium precursor materials did not have a strong impact on washcoat structural properties or on catalytic performance upon thermal aging. In fact, in both cases no phase segregation of ceria based solid solution was observed in the entire temperature range investigated. This behavior is attributed to the presence of alumina in the washcoat which acts as a diffusion barrier inhibiting solid solution grain growth that could lead to the undesirable phase segregation. Over a second stage, a systematic study was carried out in order to elucidate the influence of different oxide promoters on catalytic activity and thermal durability as well as to correlate important physicochemical properties of promoted catalysts with their three–way catalytic performance. For this purpose, catalytic powders with different ceria based solid solutions, CexZryLazOδ, were produced and properties such as microstructure, pore structure characteristics, oxygen storage capacity and noble metal dispersion in the fresh state and upon thermal aging at 900 oC in an oxidative atmosphere were evaluated. Further, cordierite monoliths were coated with the as developed powders in order to attain catalytic activity measurements under simulated exhaust conditions at the stoichiometric point. It was found that doping ceria with Zr4+ and/or La3+ cations leads to enhanced catalytic performance at the fresh state and significant stability after thermal aging. The highest activity especially in NO conversion and thermal durability was demonstrated by Pt/ACZL catalyst containing Ce0.4Zr0.5La0.1O1.95 solid solution. Correlation of the catalytic performance with physicochemical properties of the examined catalytic samples revealed that enhanced reducibility of ceria based solid solution was a much more essential parameter than the number of metal-support interfacial sites originating from the increased noble metal dispersion. Great differences among the as developed samples in terms of structural and morphological characteristics were displayed by elevating the calcination temperature at 1100 oC demonstrating the beneficial effect of mainly Zr doping on ceria’s stabilization and of La doping on alumina’s stabilization. After concluding on the optimum synthesis procedure and washcoat composition, a final effort to improve the catalytic behavior of the monometallic TWC involved alkali addition. For this reason, catalytic samples consisting of γ-alumina supports modified by two ceria based solid solutions and sodium serving as electropositive promoter, were prepared. In order to evaluate thermal durability, samples were subjected to heat treatment at the elevated temperature of 900 oC in an oxidative atmosphere and activity measurements were acquired. Catalysts with different sodium content were produced together with a reference sample with no oxide modifiers, in order to consider several issues such as optimal alkali loading, location of electropositive promoter before and after thermal treatment at an elevated temperature, synergetic effect between alkali promoter and rare earth modifiers, and finally the potential practical application of the as developed catalytic samples by comparing them with a commercial bimetallic Pt/Rh TWC with significantly higher noble metal loading. An extensive structural and textural investigation (TG/DTA, XRD, N2 adsorption, SEM, TEM analyses) was performed and correlated with catalytic activity. Electrochemical promotion resulted in remarkable improvement of catalytic properties at the fresh state along with extraordinary thermal stability. The pronounced effect of alkali addition was further elucidated by comparing the as prepared catalytic samples to the commercial bimetallic TWC. As revealed, the sample with the maximum alkali content (15 % wt) exhibited ~100 % conversion of all pollutants even after aging, whereas the activity of the commercial TWC varied between 63 –

Mesoporous CuO/TiO2 catalysts prepared by the ammonia driven deposition precipitation method for CO preferential oxidation: Effect of metal loading

Supported CuO catalysts onto a highly crystalline mesoporous TiO2 material are produced via an ammonium driven deposition precipitation method and tested for prefere degrees ntial oxidation of CO in H-2-rich gases. The effect of Cu loading on the oxidation activity is investigated by producing samples with final Cu content varying between 2.5 and 10 wt%. According to the analysis results, the chemical nature of the CuO species differs in each sample depending on the Cu loading. All materials tested are highly selective towards CO oxidation up to 160 degrees C. The 5 wt% Cu loaded material demonstrates the optimum CO-PROX performance, which is ascribed to the formation of finely dispersed and easily reducible copper oxide nanoparticles. Stability and durability of the latter sample are assessed by performing multiple testing cycles corresponding to >100hrs on stream as well as by the separate and combined addition of CO2 and H2O in the feeding stream

The effect of nano-hydroxyapatite/chitosan scaffolds on rat calvarial defects for bone regeneration

Background This study aims at determining the biological effect of 75/25 w/w nano-hydroxyapatite/chitosan (nHAp/CS) scaffolds on bone regeneration, in terms of fraction of bone regeneration (FBR), total number of osteocytes (Ost), and osteocyte cell density (CD), as well as its biodegradability. Methods Two critical-size defects (CSDs) were bilaterally trephined in the parietal bone of 36 adult Sprague-Dawley rats (18 males and 18 females); the left remained empty (group A), while the right CSD was filled with nHAp/CS scaffold (group B). Two female rats died postoperatively. Twelve, 11, and 11 rats were euthanized at 2, 4, and 8 weeks post-surgery, respectively. Subsequently, 34 specimens were resected containing both CSDs. Histological and histomorphometric analyses were performed to determine the FBR, calculated as [the sum of areas of newly formed bone in lateral and central regions of interest (ROIs)]/area of the original defect, as well as the Ost and the CD (Ost/mm(2)) in each ROI of both groups (A and B). Moreover, biodegradability of the nHAp/CS scaffolds was estimated via the surface area of the biomaterial (BmA) in the 2nd, 4th, and 8th week post-surgery. Results The FBR of group B increased significantly from 2nd to 8th week compared to group A (P = 0.009). Both the mean CD and the mean Ost values of group B increased compared to group A (P = 0.004 and P < 0.05 respectively). Moreover, the mean value of BmA decreased from 2nd to 8th week (P = 0.001). Conclusions Based on histological and histomorphometric results, we support that 75/25 w/w nHAp/CS scaffolds provide an effective space for new bone formation

A Green Route to Copper Loaded Silica Nanoparticles Using Hyperbranched Poly(Ethylene Imine) as a Biomimetic Template: Application in Heterogeneous Catalysis

Copper containing silica nanostructures are easily produced through a low cost versatile approach by means of hyperbranched polyethyleneimine (PEI), a water soluble dendritic polymer. This dendritic molecule enables the formation of hybrid organic/inorganic silica nanoparticles in buffered aqueous media, at room temperature and neutral pH, through a biomimetic silicification process. Furthermore, the derived hybrid organic/inorganic materials dispersed in water can be easily loaded with various copper amounts, due to the presence of PEI, which, despite having been integrated in the silica network, retains its strong copper chelating ability. Following calcination, the obtained copper loaded nanopowders are characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), N2 adsorption, Temperature programmed reduction (TPR) and UV-Vis diffuse reflectance (UV-Vis-DR) techniques and evaluated for automotive exhaust purification under simulated conditions at the stoichiometric point. Effective control over final materials’ pore structural and morphological characteristics is provided by employing different buffer solutions, i.e., tris(hydroxymethyl)aminomethane (Tris) or phosphate buffer. It was found that the enhancement of the nanopowders textural features, obtained in the presence of Tris buffer, had a great impact on the material’s catalytic behavior, improving significantly its activity towards pollutants oxidation

A green route to copper loaded silica nanoparticles using hyperbranched poly(ethylene imine) as a biomimetic template : application in heterogeneous catalysis

Copper containing silica nanostructures are easily produced through a low cost versatile approach by means of hyperbranched polyethyleneimine (PEI), a water soluble dendritic polymer. This dendritic molecule enables the formation of hybrid organic/inorganic silica nanoparticles in buffered aqueous media, at room temperature and neutral pH, through a biomimetic silicification process. Furthermore, the derived hybrid organic/inorganic materials dispersed in water can be easily loaded with various copper amounts, due to the presence of PEI, which, despite having been integrated in the silica network, retains its strong copper chelating ability. Following calcination, the obtained copper loaded nanopowders are characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), N2 adsorption, Temperature programmed reduction (TPR) and UV-Vis diffuse reflectance (UV-Vis-DR) techniques and evaluated for automotive exhaust purification under simulated conditions at the stoichiometric point. Effective control over final materials’ pore structural and morphological characteristics is provided by employing different buffer solutions, i.e., tris(hydroxymethyl)aminomethane (Tris) or phosphate buffer. It was found that the enhancement of the nanopowders textural features, obtained in the presence of Tris buffer, had a great impact on the material’s catalytic behavior, improving significantly its activity towards pollutants oxidation

Towards highly loaded and finely dispersed CuO catalysts via ADP : effect of the alumina support

To meet current economic demands enforcing the replacement of platinum-group metals, extensively used in three-way-catalytic converters (TWC), research is driven towards low-cost and widely available base metals. However, to cope with their lower activity, high metal loadings must be coupled with increased dispersion. Herein, a series of CuO/Al2O3 samples is produced and the effect of different alumina supports’ properties on CuO dispersion, speciation and eventually on the TWC performance is studied. The alumina samples are synthesized via different methods, including soft-templating routes and flame spray pyrolysis, and compared with a commercial one, while CuO used as the catalytic active phase is added through ammonia-driven deposition–precipitation. As found, the large surface area and low crystallinity of the aluminas produced by soft-templating routes favor strong metal–support interaction, generating highly dispersed and strongly bonded CuO species at low loading and copper-aluminate phases at high loading. Notably, the use of amorphous mesoporous alumina completely prevents the formation of crystalline CuO even at 15 wt% Cu. Such high metal loading and dispersion capacity without the application of elevated calcination temperatures is one of the best reported for nonreducible supports. Catalytic evaluation of this material reveals a pronounced enhancement of oxidation activity with metal loading increase

Towards Highly Loaded and Finely Dispersed CuO Catalysts via ADP: Effect of the Alumina Support

To meet current economic demands enforcing the replacement of platinum-group metals, extensively used in three-way-catalytic converters (TWC), research is driven towards low-cost and widely available base metals. However, to cope with their lower activity, high metal loadings must be coupled with increased dispersion. Herein, a series of CuO/Al2O3 samples is produced and the effect of different alumina supports’ properties on CuO dispersion, speciation and eventually on the TWC performance is studied. The alumina samples are synthesized via different methods, including soft-templating routes and flame spray pyrolysis, and compared with a commercial one, while CuO used as the catalytic active phase is added through ammonia-driven deposition–precipitation. As found, the large surface area and low crystallinity of the aluminas produced by soft-templating routes favor strong metal–support interaction, generating highly dispersed and strongly bonded CuO species at low loading and copper-aluminate phases at high loading. Notably, the use of amorphous mesoporous alumina completely prevents the formation of crystalline CuO even at 15 wt% Cu. Such high metal loading and dispersion capacity without the application of elevated calcination temperatures is one of the best reported for nonreducible supports. Catalytic evaluation of this material reveals a pronounced enhancement of oxidation activity with metal loading increase

An investigation of the role of Zr and La dopants into Ce1−x−yZrxLayOδ enriched γ-Al2O3 TWC washcoats

Δημοσίευση σε επιστημονικό περιοδικόSummarization: This work involves the synthesis of composite three-way catalytic (TWC) washcoats consisting of 80 wt% of γ-alumina as the main supporting material, promoted with 20 wt% of ceria based solid solution. Pt in low loading (0.5 wt%) was employed as the only active phase. Washcoats varying in the solid solution composition (CexZryLazOδ), prepared by coprecipitation, are comparatively investigated in an attempt to elucidate the effect of Ce, Zr and La oxide promoters on the catalytic activity and thermal durability. For this purpose, catalytic activity measurements as well as detailed structural and morphological evaluations (differential thermal analysis (DTA), X-ray diffraction (XRD), N2 adsorption, oxygen storage capacity and DRIFTS analyses) were carried out before and after thermal aging in oxidative atmosphere. The catalytic performance was studied in loaded cordierite monoliths (TWCs form) under simulated exhaust conditions at the stoichiometric point. Doping ceria with Zr and La cation proved beneficial for both catalytic performance and thermal durability of the washcoat, with Ce0.4Zr0.5La0.1O1.9/γ-Al2O3/Pt sample presenting the optimum properties. The catalytic behavior is discussed based on oxygen storage capacity, noble metal dispersion and textural characteristics of the examined samples.Παρουσιάστηκε στο: Applied Catalysis A: Genera