The effect of noble metal (M: Ir, Pt, Pd) on M/Ce2 O3-¿-Al2 O3 catalysts for hydrogen production via the steam reforming of glycerol

A promising route for the energetic valorisation of the main by-product of the biodiesel industry is the steam reforming of glycerol, as it can theoretically produce seven moles of H2 for every mole of C3 H8 O3. In the work presented herein, CeO2 –Al2 O3 was used as supporting material for Ir, Pd and Pt catalysts, which were prepared using the incipient wetness impregnation technique and characterized by employing N2 adsorption–desorption, X-Ray Diffraction (XRD), Temperature Programmed Reduction (TPR), Temperature Programmed Desorption (TPD), X-ray Photoelectron Spectroscopy (XPS) and Transmission Electron Microscopy (TEM). The catalytic experiments aimed at identifying the effect of temperature on the total conversion of glycerol, on the conversion of glycerol to gaseous products, the selectivity towards the gaseous products (H2, CO2, CO, CH4) and the determination of the H2 /CO and CO/CO2 molar ratios. The main liquid effluents produced during the reaction were quantified. The results revealed that the Pt/CeAl catalyst was more selective towards H2, which can be related to its increased number of Brønsted acid sites, which improved the hydrogenolysis and dehydrogenation–dehydration of condensable intermediates. The time-on-stream experiments, undertaken at low Water Glycerol Feed Ratios (WGFR), showed gradual deactivation for all catalysts. This is likely due to the dehydration reaction, which leads to the formation of unsaturated hydrocarbon species and eventually to carbon deposition. The weak metal–support interaction shown for the Ir/CeAl catalyst also led to pronounced sintering of the metallic particles

Biogas dry reforming over Ni/LnOx-type catalysts (Ln = La, Ce, Sm or Pr)

Ni/LnOx-type catalysts (Ln = La, Ce, Sm or Pr, denoted as LNO, CNO, SNO and PNO, respectively) were prepared via a citrate sol-gel method, characterized, and evaluated for the dry reforming of biogas. For the calcined catalysts, the formation of LaNiO3 perovskite crystallites with high purity was observed in the case of La, whereas NiO-LnOx mixed oxides were obtained for the other lanthanides. The reduction treatment led to the formation of medium-sized (∼15 nm) and highly dispersed Ni nanoparticles in LNO following the decomposition of the LaNiO3 perovskite, in contrast to the other catalysts, where bigger Ni crystallites were formed (∼30 nm). As a result, LNO was shown to possess a higher catalytic activity in comparison to the other materials. Regarding the catalytic stability, LNO displayed a considerable activity loss followed by a high pressure drop due to reactor blockage, meaning that the use of Sm (Ni/Sm2O3) can be considered as an alternative strategy to restrict catalyst deactivation. As evidenced by the characterization of the spent catalysts, the deactivation for the most part can be attributed to the extensive coke deposition over the catalysts. The coke deposited was found to be both in the form of more disordered/amorphous carbon, as well as in the form of highly crystalline and multi-walled carbon nanotubes.The authors gratefully acknowledge the Ministry of Science and Technology (MOST) of the People's Republic of China providing funds through the National Key Research and Development Program (project code:2017YFE013330). The authors also gratefully acknowledge that this research has been co-financed by the European Union and Greek national funds under the call “Greece – China Call for Proposals for Joint RT&D Projects” (Project code: T7DKI-00388). V.S. acknowledges the assistance of the Laboratorio de Microscopias Avanzadas-LMA-ICTS ELECMI, Universidad de Zaragoza, Spain. CIBER-BBN is an initiative funded by the VI National R&D&i Plan 2008–2011 financed by the Instituto de Salud Carlos III with the assistance of the European Regional Development Fund.Peer reviewe

Σύνθεση, χαρακτηρισμός και αξιολόγηση καινοτόμων στερεών καταλυτικών συστημάτων για την παραγωγή αιθυλενίου μέσω της αντίδρασης της οξειδωτικής σύζευξης μεθανίου

This dissertation presents new experimental results and information on the production of C2H4 through the reaction of oxidative coupling of methane (OCM). Methane may be derived either from raw biomass, or from waste treatment, or from natural gas. Ethylene is a highly valuable raw material in the petrochemical industry, as it can be used for the production of polymers (e.g., polyethylene), but also many other added-value products. For the PhD thesis presented herein, the OCM process has been investigated using un - modified and modified cerium-based catalysts, using simultaneously methane and oxygen as feed. The reaction was carried out at atmospheric pressure, between 600 and 870oC. In addition to the OCM process, the adsorption (and desorption) of ethylene and the valorization of CO2 via the CO2 hydrogenation reaction were also studied. Both of the aforementioned processes make use of the gaseous products of the oxidation coupling of CH4, i.e., C2H4, C2H6, CH4, CO2 and CO, and may help increase the overall efficiency of the reaction. Thus, this dissertation focuses on the study of CH4 and CO2 as raw materials, in order to achieve ambitious results (high yield of value-added products) through highly efficient catalytic processes and innovative catalytic materials. To meet these challenges, this dissertation had to cover modern research areas, through the use of new innovative preparation methods of highly active catalytic systems with improved structural, physicochemical properties (dispersion of active sites, acid-base properties, O2 storage capacity), reinforcing the yield and selectivity in terms of the desirable products. In particular, the dissertation contributes five independent and innovative research studies (i.e., publications in international, peer reviewed journals), which concern: (a) the experimental and theoretical investigation of the adsorption of C2H4 from a mixture that simulates the products obtained during the OCM process, using a commercial molecular sieve; (b) the preparation, characterization and investigation of the catalytic activity and stability in the OCM reaction of modified and/or un-modified lithium (Li+) catalysts based on cerium oxide (CeO2) supporting materials; and (c) the preparation, characterization and investigation of the catalytic activity and durability in the reaction of CO2 methanation of nickel (Ni) catalysts based on modified and/or un-modified CeO2 supporting materials.Η παρούσα διδακτορική διατριβή παρουσιάζει πρωτότυπα πειραματικά αποτελέσματα και νέες πληροφορίες για την παραγωγή C2H4 μέσω της αξιοποίησης του μεθανίου, είτε αυτό προέρχεται από πρωτογενή βιομάζα, είτε από επεξεργασία απορριμμάτων, είτε από το φυσικό αέριο. Είναι γνωστό ότι το C2H4 χρησιμοποιείται ως ενισχυτής για την ωρίμανση των φρούτων και ως πρώτη ύλη στην πετροχημική βιομηχανία για την παραγωγή πολυμερών (π.χ. πολυαιθυλένιο), αλλά και πολλών άλλων βασικών προϊόντων. Για την υλοποίηση του παραπάνω στόχου μελετήθηκε η αντίδραση της οξειδωτικής σύζευξης του μεθανίου (ΟΣΜ) παρουσία καταλυτών στηριζόμενων σε ενισχυμένα ή μη οξείδια του δημητρίου (CeO2), υπό συνθήκες ταυτόχρονης τροφοδοσίας μεθανίου και οξυγόνου, σε ατμοσφαιρική πίεση και σε θερμοκρασιακό εύρος μεταξύ 600-870οC. Επιπρόσθετα, στα πλαίσια της διδακτορικής διατριβής, μελετήθηκε η διεργασία της προσρόφησης – εκρόφησης του C2H4, όπως και η αξιοποίηση του CO2 μέσω της αντίδρασης της υδρογόνωσης για την παραγωγή συνθετικού φυσικού αερίου. Υπενθυμίζεται ότι τα προϊόντα αντίδρασης της ΟΣΜ αποτελούνται από C2H4, C2H6, CH4, CO2 και CO. Το βασικό ενδιαφέρον αυτής της διατριβής εστιάζεται στη μελέτη του CH4, αλλά και του CO2 ως πρώτη ύλη για την επίτευξη ωφέλιμων αποτελεσμάτων (παραγωγή χρήσιμων χημικών προϊόντων αυξημένης προστιθέμενης αξίας) μέσω καταλυτικών διεργασιών και προηγμένων καταλυτικών υλικών. Για την επίτευξη αυτών των προκλήσεων, η θεματολογία της διατριβής πηγάζει από τομείς της σύγχρονης έρευνας όπως αυτοί της προώθησης της ενεργότητας των καταλυτών και της χρήσης διαφορετικών μεθόδων παρασκευής καταλυτικών συστημάτων με βελτιωμένες δομικές και φυσικοχημικές ιδιότητες (διασπορά ενεργού φάσης, οξεοβασικές ιδιότητες, ικανότητα αποθήκευσης οξυγόνου) για την ενίσχυση της απόδοσης και της εκλεκτικότητας τους ως προς τα επιθυμητά προϊόντα. Σε πειραματικό επίπεδο, η διατριβή συνεισφέρει πέντε ανεξάρτητες και πρωτότυπες μελέτες (ήτοι, δημοσιευμένες εργασίες σε διεθνή περιοδικά με κριτές) οι οποίες αφορούν: (α) τη πειραματική και θεωρητική μελέτη της προσρόφησης του C2H4 από ένα μείγμα που προσομοιώνει τα προϊόντα που λαμβάνονται κατά την αντίδραση ΟΣΜ (κυρίως CO2, CO, CH4, C2H4 και C2H6), χρησιμοποιώντας ένα εμπορικό μοριακό κόσκινο (MOS), (β) τη παρασκευή, τον χαρακτηρισμό και τη μελέτη της δραστικότητας και σταθερότητας καταλυτικών συστημάτων με ενεργό φάση το Λίθιο (Li+) στηριγμένων σε φορέα CeO2 τροποποιημένο ή μη στην αντίδρασης της ΟΣΜ, και (γ) τη παρασκευή, το χαρακτηρισμό και την αξιολόγηση της απόδοσης και του χρόνου ζωής στην αντίδραση της υδρογόνωσης του CO2 ως προς την παραγωγή CH4, καταλυτών νικελίου (Ni) στηριζόμενους σε φορέα CeO2 τροποποιημένο ή μη

Structural Investigation of the Carbon Deposits on Ni/Al2O3 Catalyst Modified by CaO-MgO for the Biogas Dry Reforming Reaction

Ni catalysts based on Al2O3 and Al2O3 modified with CaO-MgO were tested for the dry reforming of biogas (BDR). Time-on-stream experiments were carried out between 600 and 800 °C, and the spent catalysts were examined using a variety of characterization techniques including, N2 adsorption/desorption, thermogravimetric analysis (TGA), Raman spectroscopy, electron microscopy (STEM-HAADF and HR-TEM), and X-ray photoelectron spectroscopy (XPS). It was revealed that the carbon deposits consisted of carbon nanotubes and amorphous carbon for both samples. XPS studies showed the presence of Ni0 on both catalysts and Ni2O3/NiAl2O4 on the Ni/Al2O3 sample. The time-on-stream experiments showed that the Ni/CaO-MgO-Al2O3 catalyst is more resistant to deactivation and more active and selective for all temperatures under investigation. It was concluded that doping Al2O3 with CaO-MgO enhances catalytic performance as: (a) it helps to maintain highly dispersed Ni0 during the BDR as the interaction between metal and support is a stronger one, (b) it leads to the formation of carbon structures that are easier to oxidize, and (c) it facilitates the gasification of the carbon deposits because its increased surface basic sites enhance the adsorption of carbon dioxide

Effect of Active Metal Supported on SiO2 for Selective Hydrogen Production from the Glycerol Steam Reforming Reaction

The performance of nickel, cobalt, and copper supported on silica as catalysts was evaluated for the glycerol steam reforming (GSR) reaction. The samples were characterized by nitrogen-porosimetry according to Brunauer-Emmett-Teller (BET) method, X-ray diffraction (XRD), and inductively coupled plasma atomic emission spectroscopy (ICP-AES), while the deposited carbon on the catalytic surface was measured with a CHN-analyzer. Catalysts were studied in order to investigate the effect of the reaction temperature on (i) glycerol total conversion, (ii) glycerol conversion to gaseous products, (iii) hydrogen selectivity and yield, (iv) selectivity of gaseous products, and (v) selectivity of liquid products. The results showed that the Ni based on silica (Ni/Si) catalyst was more active and produced less liquid effluents than the catalysts that used an active metal such as Co or Cu. Moreover, the H2 yield from the Ni/Si catalyst was very close to the theoretical maximum predicted by thermodynamics, and the CO2 production was favoured in comparison to CO production, which is important for use in fuel cells

The effect of noble metal (M: Ir, Pt, Pd) on M/Ce2 O3-\u3b3-Al2 O3 catalysts for hydrogen production via the steam reforming of glycerol

A promising route for the energetic valorisation of the main by-product of the biodiesel industry is the steam reforming of glycerol, as it can theoretically produce seven moles of H2 for every mole of C3 H8 O3. In the work presented herein, CeO2 \u2013Al2 O3 was used as supporting material for Ir, Pd and Pt catalysts, which were prepared using the incipient wetness impregnation technique and characterized by employing N2 adsorption\u2013desorption, X-Ray Diffraction (XRD), Temperature Programmed Reduction (TPR), Temperature Programmed Desorption (TPD), X-ray Photoelectron Spectroscopy (XPS) and Transmission Electron Microscopy (TEM). The catalytic experiments aimed at identifying the effect of temperature on the total conversion of glycerol, on the conversion of glycerol to gaseous products, the selectivity towards the gaseous products (H2, CO2, CO, CH4) and the determination of the H2 /CO and CO/CO2 molar ratios. The main liquid effluents produced during the reaction were quantified. The results revealed that the Pt/CeAl catalyst was more selective towards H2, which can be related to its increased number of Br\uf8nsted acid sites, which improved the hydrogenolysis and dehydrogenation\u2013dehydration of condensable intermediates. The time-on-stream experiments, undertaken at low Water Glycerol Feed Ratios (WGFR), showed gradual deactivation for all catalysts. This is likely due to the dehydration reaction, which leads to the formation of unsaturated hydrocarbon species and eventually to carbon deposition. The weak metal\u2013support interaction shown for the Ir/CeAl catalyst also led to pronounced sintering of the metallic particles

Highly selective and stable nickel catalysts supported on ceria promoted with Sm2O3, Pr2O3 and MgO for the CO2 methanation reaction

[Display omitted]•Microwave assisted sol gel method produces selective CO2 methanation Ni catalysts.•The incorporation of Sm3+ and Pr3+ into the CeO2 lattice generates basic positions.•Sm3+ and Pr3+ oxygen vacancies suppress the agglomeration of Ni sites.•Presence of Mg2+ increases basicity and prevents Ni sintering during reaction.•Ni on Pr-Ce highly active, selective and stable for CO2 methanation reaction.The present work reports on the investigation of the catalytic performance for the methanation of CO2 over Ni catalysts based on CeO2, and for the first time, of Ni catalysts supported on binary CeO2-based oxides, namely, Sm2O3-CeO2, Pr2O3-CeO2 and MgO-CeO2. The supports were obtained using the microwave assisted sol-gel method under reflux, while the catalysts were prepared by the wet impregnation method. For the investigation of the morphological, textural, structural and other intrinsic properties of the catalytic materials a variety of characterization techniques were used, i.e., Raman spectroscopy, XRD, N2 physisorption-desorption, CO2-TPD, H2-TPR, H2-TPD, XPS and TEM. Carbon deposition and sintering were investigated using TEM. It was shown that the addition of Sm3+ or Pr3+, incorporated into the lattice of CeO2, generated oxygen vacancies, but the Ni/Pr-Ce catalyst was found to possess more surface oxygen vacancies (e.g. Ce4+-Ov-Pr3+ entities). Moreover, modification of CeO2 using Sm3+ or Pr3+ restricted the agglomeration of nickel active sites and led to the genesis of Lewis basic positions. These characteristics improved the hydrogenation reaction at lower temperature. On the other hand, the addition of Mg2+ resulted at strong metal support interactions reinforcing the resistance of the Ni/Mg-Ce catalyst against sintering. Furthermore, the addition of Sm3+, Pr3+ and Mg2+ cations increased the overall basicity and the moderate adsorption sites and led to the formation of smaller Ni nano particles; these physico-chemical properties enhanced the CO2 methanation reaction. Finally, the activity experiments (WGHSV = 25,000 mL g−1 h−1, H2/CO2 = 4:1, T =350 °C) showed that at lower reaction temperature the Ni/Pr-Ce had the highest catalytic performance in terms of CO2 conversion (54.5%) and CH4 yield (54.5%) and selectivity (100%). The TOF values were found to follow the order Ni/Pr-Ce >> Ni/Mg-Ce > Ni/Sm-Ce > Ni/Ce

Cerium oxide catalysts for oxidative coupling of methane reaction: Effect of lithium, samarium and lanthanum dopants

The work presented herein reports on the oxidative coupling of methane (OCM) performance of a series of Li-free and Li-doped CeO2 and CeO2 modified with Sm3+ and La3+ catalysts. The supporting materials (Ce, Sm-Ce and La-Sm-Ce metal oxides) were synthesized using the microwave assisted sol-gel method in order to achieve nanophase complex materials with increased particle surface energy and reactivity. Lithium ions were added, using the wet impregnation technique, in order to further improve the physicochemical characteristics and reinforce the activity and selectivity, in terms of C2H6 and C2H4 production. All materials were characterized using N2 adsorption-desorption, XRD, Raman spectroscopy, CO2-TPD, H2-TPR, SEM and XPS. We showed that the addition of lithium species changed the reaction pathway and drastically enhanced the production of ethylene and ethane, mainly for the promoted catalysts (Li/Sm-Ce and Li/La-Sm-Ce). In particular, the presence and the synergy between the electrophilic oxygen species (peroxide and superoxide), population of oxygen vacancy sites and the surface moderate basic sites determined the reaction pathway and the desirable product distribution

Glycerol Steam Reforming for Hydrogen Production over Nickel Supported on Alumina, Zirconia and Silica Catalysts

The aim of the work was to investigate the influence of support on the catalytic performance of Ni catalysts for the glycerol steam reforming reaction. Nickel catalysts (8 wt%) supported on Al2O3, ZrO2, SiO2 were prepared by the wet impregnation technique. The catalysts’ surface and bulk properties, at their calcined, reduced and used forms, were determined by ICP, BET, XRD, NH3-TPD, CO2-TPD, TPR, XPS, TEM, TPO, Raman, SEM techniques. The Ni/Si sample, even if it was less active for T <600 °C, produces more gaseous products and reveals higher H2 yield for the whole temperature range. Ni/Zr and Ni/Si catalysts facilitate the WGS reaction, producing a gas mixture with a high H2/CO molar ratio. Ni/Si after stability tests exhibits highest values for total (70%) and gaseous products (45%) glycerol conversion, YH2 (2.5), SH2 (80%), SCO2 (65%), H2/CO molar ratio (6.0) and lowest values for SCO (31%), SCH4 (3.1%), CO/CO2 molar ratio (0.48) among all samples. The contribution of the graphitized carbon formed on the catalysts follows the trend Ni/Si (I D /I G = 1.34) < Ni/Zr (I D /I G = 1.08) < Ni/Al (I D /I G = 0.88) and indicates that the fraction of different carbon types depends on the catalyst’s support nature. It is suggested that the type of carbon is rather more important than the amount of carbon deposited in determining stability. It is confirmed that the nature of the support affects mainly the catalytic performance of the active phase and that Ni/SiO2 can be considered as a promising catalyst for the glycerol steam reforming reaction

The influence of SiO2 doping on the Ni/ZrO2 supported catalyst for hydrogen production through the glycerol steam reforming reaction

The glycerol steam reforming (GSR) reaction for H2 production was studied comparing the performance of Ni supported on ZrO2 and SiO2-ZrO2 catalysts. The surface and bulk properties were determined by ICP, BET, XRD, TPD, TPR, TPO, XPS, SEM and STEM-HAADF. It was suggested that the addition of SiO2 stabilizes the ZrO2 monoclinic structure, restricts the sintering of nickel particles and strengthens the interaction between Ni2+ species and support. It also removes the weak acidic sites and increases the amount of the strong acidic sites, whereas it decreases the amount of the basic sites. Furthermore, it influences the gaseous products’ distribution by increasing H2 yield and not favouring the transformation of CO2 in CO. Thus, a high H2/CO ratio can be achieved accompanying by negligible value for CO/CO2. From the liquid products quantitative analysis, it was suggested that acetone and acetaldehyde were the main products for the Ni/Zr catalyst, for 750oC, whereas for the Ni/SiZr catalyst allyl alcohol was the only liquid product for the same temperature. It was also concluded that the Ni/SiZr sample seems to be more resistant to deactivation however, for both catalysts a substantial amount of carbon exists on the catalytic surface in the shape of carbon nanotubes and amorphous carbon