Study And Evaluation Of Innovative Methods For Printing Solid Catalysts Intended For NOx Pollution Control

The present Doctoral Dissertation concerns the evaluation and development of an innovative method for preparing solid supported-Pt catalysts intended for NOx pollution control. In particular, the alternative and cutting-edge approach of developing catalysts via multilayer inkjet printing was examined, so as to control the structure of solid catalysts at a nanoscale level, using two different printers, i.e., a modified Epson L800 printer and a commercial material printer (DMP-2850). For the first time ever, one 0.1 wt% Pt/MgO/CeO2 and two 0.1 wt% Pt/Al2O3 catalysts were prepared by novel inkjet printing and compared, in terms of their catalytic behaviour towards the NO/H2/O2 reaction, against four catalysts prepared by a standard and a modified wet impregnation method. It is worth mentioning that the inkjet-printed Pt/Al2O3 catalysts presented excellent activity and wide operating temperature window (TR=100-250oC) towards the selective catalytic reduction of NO by H2 under strongly oxidizing conditions (H2-SCR) in the very low-temperature range of 100-200ºC. Specifically, the Epson printed Pt/Al2O3 catalyst, presented XNO= 91% at 150oC, while the DMP printed Pt/Al2O3 catalyst presented an average XNO= 97% for the low-temperature range of 140-200oC and XNO= 99.5% at 175oC. As for the DMP inkjet-printed Pt/MgO/CeO2 catalyst, it showed remarkable catalytic performance (XNO= 100%, SN2= 100%, TR≥ 200oC) in the absence of oxygen (NO/H2 reaction), a result which has never been reported before, according to the author’s knowledge, in particular without the formation of NH3 as a by-product. Surface reactivity studies by transient methods performed within the present work indicated that the inkjet printing process leads to a unique surface structure of the printed catalysts that probably favours the formation of different intermediate NOx species, which are active at very low reaction temperatures. Moreover, it was proven through combined SSITKA-DRIFTS studies, that the different catalyst preparation methods utilized for the development of Pt/MgO-CeO2 catalysts, affects the formation and concentration of different active adsorbed intermediate NOx species on Pt surface, as well as on the support and the metal-support interphase. Furthermore, the transient experiments revealed important information towards the understanding of basic mechanistic issues of the present catalytic system (e.g., surface coverage of NOx intermediate species and N-containing species, H2 spillover).Ioannis Yentekakis, Charis TheocharisComplete

Regulating the catalytic properties of Pt/Al2O3 through nanoscale inkjet printing

For the first time ever, a 0.1 wt% Pt/Al2O3 catalyst was prepared by novel inkjet printing and compared against two catalysts prepared by a standard and modified wet impregnation method. The printed catalyst was found to present excellent activity and wide operating temperature window on the selective catalytic reduction of NO by H2 under strongly oxidizing conditions (H2-SCR) in the very low-temperature range of 100–200 °C. The transient studies performed in the present work indicated that the printing process followed led to a unique surface structure of the printed catalyst that probably favors the formation of different active intermediate NOx species, which are active at very low reaction temperatures. Moreover, it was found that the inkjet printing protocol followed resulted in a relatively uniform nano-spherical structure of the developed catalyst

Biowaste-based biochar: A new strategy for fermentative bioethanol overproduction via whole-cell immobilization

This work explores the potential use of biochar as a microbial cell carrier enhancing the efficiency of alcoholic fermentations. Olive kernels, vineyard prunings, sewage sludge and seagrass residues were applied as biowaste for biochar production through pyrolysis at two different temperatures (250 °C and 500 °C), while a commercial type of non-biomass char was also employed for benchmarking purposes. Apart from vineyard prunings pyrolyzed at 250 °C, all other carbonaceous materials presented crystalline phases including halite, calcite, sylvite and/or silicon. Moreover, increase in pyrolysis temperature enhanced biochar's porosity and BET-specific surface area, which reached 41.7 m 2 g −1 for VP-based biochar remaining at lower levels (0.15–5.3 m 2 g −1 ) in other specimens tested. Elemental analysis demonstrated reduction in oxygen and increase in the carbon content of biochars produced at elevated temperatures, while biochar from seagrass included residues of chloride (0.3–5.14%). Three major yeasts were immobilized on materials exhibiting the highest surface areas and applied in repeated batch fermentations using Valencia orange peel hydrolyzates as feedstock. The biocatalysts developed using S. cerevisiae and K. marxianus immobilized on vineyard prunings-based biochar exhibited exceptional ethanol productivities as compared to the relevant literature, which reached 7.2 g L −1 h −1 and 7.3 g L −1 h −1 respectively. Although the aforementioned strains improved biofuel production by 36–52% compared to the conventional process, P. kudriavzevii KVMP10 was not efficient following immobilization on biochar. The approach constitutes an innovative method for bioenergy production, demonstrating a novel application of biochar in industrial biotechnology which incorporates important technological advances such as enhanced biofuel production and biomass recycling

Biowaste-based biochar: A new strategy for fermentative bioethanol overproduction via whole-cell immobilization

This work explores the potential use of biochar as a microbial cell carrier enhancing the efficiency of alcoholic fermentations. Olive kernels, vineyard prunings, sewage sludge and seagrass residues were applied as biowaste for biochar production through pyrolysis at two different temperatures (250 °C and 500 °C), while a commercial type of non-biomass char was also employed for benchmarking purposes. Apart from vineyard prunings pyrolyzed at 250 °C, all other carbonaceous materials presented crystalline phases including halite, calcite, sylvite and/or silicon. Moreover, increase in pyrolysis temperature enhanced biochar's porosity and BET-specific surface area, which reached 41.7 m 2 g −1 for VP-based biochar remaining at lower levels (0.15–5.3 m 2 g −1 ) in other specimens tested. Elemental analysis demonstrated reduction in oxygen and increase in the carbon content of biochars produced at elevated temperatures, while biochar from seagrass included residues of chloride (0.3–5.14%). Three major yeasts were immobilized on materials exhibiting the highest surface areas and applied in repeated batch fermentations using Valencia orange peel hydrolyzates as feedstock. The biocatalysts developed using S. cerevisiae and K. marxianus immobilized on vineyard prunings-based biochar exhibited exceptional ethanol productivities as compared to the relevant literature, which reached 7.2 g L −1 h −1 and 7.3 g L −1 h −1 respectively. Although the aforementioned strains improved biofuel production by 36–52% compared to the conventional process, P. kudriavzevii KVMP10 was not efficient following immobilization on biochar. The approach constitutes an innovative method for bioenergy production, demonstrating a novel application of biochar in industrial biotechnology which incorporates important technological advances such as enhanced biofuel production and biomass recycling

Novel catalytic and mechanistic studies on wastewater denitrification with hydrogen

Presented at: IWA Regional Conference on Waste and Wastewater Management, Science and Technology, 2013, Limassol, Cyprus, 26-28 JuneThe present work reports up-to-date information regarding the reaction mechanism of the catalytic hydrogenation of nitrates in water media. In the present mechanistic study, an attempt is made, for the first time, to elucidate the crucial role of several catalysts and reaction parameters in the mechanism of the NO3-/H2 reaction. Steady-state isotopic transient kinetic analysis (SSITKA) experiments coupled with ex situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) were performed on supported Pd-Cu catalysts for the NO3-/H2 and NO3-/H2/O2 reactions. The latter experiments revealed that the formation and surface coverage of various adsorbed active intermediate N-species on the support or Pd/Cu metal surface is significantly favored in the presence of TiO2 in the support mixture and in the presence of oxygen in the reaction's gaseous feed stream. The differences in the reactivity of these adsorbed N-species, found in the present work, adequately explain the large effect of the chemical composition of the support and the gas feed composition on catalyst behaviour (activity and selectivity). The present study leads to solid mechanistic evidence concerning the presence of a hydrogen spillover process from the metal to the support. Moreover, this study shows that Cu clusters are active sites for the reduction of nitrates to nitrites

The effect of several parameters on catalytic denitrification of water by the use of H2 in the presence of O2 over metal supported catalysts

The present paper involves a detailed study of the selective catalytic reduction of nitrates in aqueous mediums by the use of H2 in the presence of O2 over monometallic and bimetallic supported catalysts. In this study, an attempt has been made to improve the denitrification efficiency (XNO3-, SN2) of several catalysts by regulating some experimental parameters that are involved in the process. Therefore, the effects of the type of reactor (semi-batch reactor vs continuous flow reactor), the nature of the active phase (Pd, Cu, and Pd-Cu) and the particle size of γ-Al2O3 spheres (particle diameter= 1.8 mm and 3 mm) on catalytic activity and reaction selectivity, as well as the adsorption capacity of γ-Al2O3 spheres for nitrates, were examined. As the review indicates, most of the research has so far been conducted on batch or semi-batch reactors. This study successfully demonstrates the benefits of using a continuous flow reactor in terms of catalytic activity (XNO3-, %) and reaction selectivity (SN2, %). Another important aspect of this study is the crucial role of bimetallic Pd-Cu clusters for the prevention of NH4+ formation. Moreover, the use of 1.8 mm diameter γ-Al2O3 spheres as a support was proved to significantly enhance the catalytic performance of bimetallic Pd-Cu catalysts towards nitrate reduction compared to 3 mm diameter γ-Al 2O3 spheres. This difference may be attributed to mass (NO3-, OH-) transfer effects (external mass transfer phenomena)