Preparation of thermally stable geopolymers as new catalysts or supports

Geopolymers are alkali bonded ceramics (ABC\u27s) and are produced using an energy saving process involving chemical reactions in aqueous medium at T < 120?C. Thermally stable geopolymers may have many industrial applications, considering that their preparation allows to produce near-net-shape pieces, also simultaneously to the foaming. ABC\u27s have a three-dimensional aluminosilicate network, in which polymeric Si-O-Al-O bonds form under alkaline conditions in presence of aluminosilicates. The final structure of a fully reacted ABC consists of nanoparticulates ranging from 5 to 15 nm, pores of 3 to 10 nm with specific surface area in the range 20-140 m2/g. Finally, the functional and structural properties of the ABC\u27s can be tailored by introducing specific ceramic fillers. The geopolymer network and the zeolite framework have close similarity in the exchange with charge balancing cations; ABC\u27s network also enables incorporation of transition metal ions or protonic extra-network sites as active centres for catalytic reactions. However, it must be noted that geopolymers posses some advantages in comparison to zeolites, such as formation at room or low temperature, mesoporosity and low preparation cost, opening potential interests for the synthesis of new robust catalysts for heterogeneous reactions. Aim of this study was to set up the preparation method for new geopolymers (pellets and/or foams) to be applied as catalysts or support

High-Temperature ceramic coatings with geopolymeric binders

High-temperature (HT) resistant coatings represent an updating subject of high industrial interest on account of their relevant applications (turbines, engines, aeronautic, ecc.). While many HT resistant products are known, not simple appears to satisfy the requirement of their high and stable adhesion on the support. The aim of this work was to develop novel HT resistant ceramic coatings based on silicon carbide and/or zirconium oxide, using geopolymeric resins as binders. Geopolymers show many advantages respect to organic polymers, first of all their high heat resistance and refractoriness. Moreover, they are fully inorganic, do not require organic solvents and are not off-gassing. During the geopolymerization step, the polymineral resin (alumino-silicate binders) is formed, acting as glue sticking together the unreacted Al-Si source materials and fillers (ceramic powders), forming the ceramic-geopolymer composite coatings. In order to optimize the geopolimeric binders, different raw materials have been tested (caolins, meta-kaolins and alumina/silica fine powders), while the alkali aqueous solution was KOH/K2SiO3, fixing the ratios SiO2/Al2O3 = 4 and SiO2/K2O = 2. Setting conditions, microstructural evolution as a function of the temperature and thermal evolution either in air or inert atmosphere were deeply investigated in order to set-up the best preparation conditions. HT resistant coatings were prepared by mixing the ceramic fillers (90 wt%) with geopolimeric binders, then applying the obtained mixture on ceramic substrates by brushing. After a first setting, coatings were stabilized by a thermal treatment in inert atmosphere at 1350?C and then the oxidation behaviour and adhesion level on the substrates were studied. A key role of new glass-ceramic phases formed during the thermal treatments has been evidenced

Geopolymer-zeolite composites for CO2 adsorption

Geopolymer-zeolite composites were produced mixing different geopolymer matrices with a synthetic commercial Na13X zeolite, to combine the functional microporosity of the zeolite with the mesoporosity of the geopolymer matrix, with the further possibility to consolidate the zeolite powder. The new materials were designed and produced in forms of monoliths to be used as adsorbents for low temperature CO2 capture applications. A potassium or sodium silicate activating solution was used to produce the metakaolin-based geopolymer matrices, then mixed with the synthetic zeolite used as a filler. As geopolymers can be regarded as the amorphous counterpart or precursor of crystalline zeolites, it is important to underline the chemical affinity between these two constituents. As a matter of fact, the morphological characterization evidenced the presence of geopolymer nanoprecipitates covering zeolite particles for the K-based composite, while in the Na-based composite the formation of a NaA zeolite phase was evidenced (Fig. 1). Please click Additional Files below to see the full abstract

Catalytic upgrading of clean biogas to synthesis gas

Clean biogas, produced by anaerobic digestion of biomasses or organic wastes, is one of the most promising substitutes for natural gas. After its purification, it can be valorized through different reforming processes that convert CH4 and CO2 into synthesis gas (a mixture of CO and H2). However, these processes have many issues related to the harsh conditions of reaction used, the high carbon formation rate and the remarkable endothermicity of the reforming reactions. In this context, the use of the appropriate catalyst is of paramount importance to avoid deactivation, to deal with heat issues and mild reaction conditions and to attain an exploitable syngas composition. The development of a catalyst with high activity and stability can be achieved using different active phases, catalytic supports, promoters, preparation methods and catalyst configurations. In this paper, a review of the recent findings in biogas reforming is presented. The different elements that compose the catalytic system are systematically reviewed with particular attention on the new findings that allow to obtain catalysts with high activity, stability, and resistance towards carbon formation

Chemical Looping Combustion in a Bed of Iron Loaded Geopolymers

Abstract The chemical looping combustion allows for inherent CO 2 separation when burning fossil fuels in presence of a suitable oxygen carrier. The choice of the material to be used should take into account not only chemical/physical properties but also economical, environmental, and safety concerns, addressing for more common materials, like Fe oxides. In this research a geopolymeric oxygen carrier, based on Fe 2 O 3 , was tested for the first time in a laboratory CLC plant operated at high temperature for the combustion of a CO rich gas from char gasification in CO 2 . The CLC plant reliably performed in repeated cycles without decay of the CO conversion during the chemical looping combustion. The maximum CO content in the flue gas was around 1% vol. and carbon monoxide conversion achieved 97%. The calculated oxygen transport capacity was 0.66%. The plant results were confirmed by the XRD analysis that proved the presence of reduced phases in samples after chemical looping stage and by significant peaks obtained during H 2 reduction in TPR equipment

Ru–CeO2 and Ni–CeO2 Coated on Open-Cell Metallic Foams by Electrodeposition for the CO2 Methanation

CO2 methanation structured catalysts, made by a layer of Ru–CeO2 or Ni–CeO2 (Ru/Ce = 3/97; Ni/Ce = 1/3 and 3/1) on open-cell NiCrAl foams, are prepared by electrodeposition and a subsequent calcination step. The performance of the catalysts at a space velocity of 320,000 mL gcat–1 h–1 in a feedstock with H2/CO2/N2 = 4/1/1 v/v, significantly depends on the Ni content and the preparation method. A low Ru or Ni content promotes the metal–CeO2 interaction, the formation of defects in CeO2 as well as the development of a lower amount of cracks in the coating; however, the catalysts show a poor CO2 conversion and selectivity to CH4. The CH4 production rate at low temperature largely increases for the high Ni loaded catalyst, 68.7 LCH4 gNi–1 h–1 at 350 °C oven temperature. This productivity is similar to the value obtained with a Ni3Ce1 pellet catalyst prepared by the coprecipitation method, a behavior not achievable for low Ru- and Ni-loaded catalysts

Synthesis and properties of new geopolymeric foams

Geopolymers are innovative, versatile and cheap inorganic materials with a wide number of industrial applications, having, furthermore, obtained in environmentally friendly conditions [1]. In previous papers, the synthesis and thermal stability of geopolymers were deeply investigated [2,3]; the aim of this study was to develop new geopolymeric foams with tailored porosity in the nano-ultramacro range, in the view of potential applications in the thermal insulation, catalysis, filtration, biomaterials, etc. Geopolymers have been prepared starting from metakaolin and potassium silicate; the process conditions were varied to change the intrinsic nano-micro-porosity of the material and study their influence on the geopolymerization degree. Optimum geopolymerization conditions were selected to develop porous 3D networks by inducing interconnected ultra-macro-porosity (up to millimetric range) in the material, exploiting the ability of Si powder to generate H2 by reaction with H2O (Fig. 1). The in situ foaming was strongly dependent on H2O content of the precursors and the successive process of H2O elimination. The H2 formation is in fact a H2O consuming process, thus increasing the viscosity, as consolidation occurs. The geopolymeric inorganic resins and the related foams were fully characterized in term of microstructure, intrinsic and induced porosity size distribution, specific surface area, geopolymerization degree and surface accessibility. The thermal behavior of the materials was also deeply investigated. The experimental findings highlighted the versatility of these foams, that may be properly tailored as a function of the possible final applicatio

Promotion effect of rare earth elements (Ce, Nd, Pr) on physicochemical properties of M-Al mixed oxides (M = Cu, Ni, Co) and their catalytic activity in N2O decomposition

A series of M-AlOx mixed oxides (M = Cu, Co, Ni) with the addition of high loadings of rare earth elements (REE, R = Ce, Nd, Pr; R0.5M0.8Al0.2, molar ratio) were investigated in N2O decomposition. The precursors were prepared by coprecipitation and subsequent calcination at 600\ua0\ub0C. The obtained mixed metal oxides were characterized by X-ray diffraction with Rietveld analysis, N2 sorption, and H2 temperature-programmed reduction. Depending on the nature of REE and the initial M-Al system, R cations could be separately segregated in oxide form or coordinated with the transition metal cations and form mixed structures. The addition of Ce3+ consistently led to nanocrystalline CeO2 mixed with the divalent oxides, whereas the addition of Nd3+ or Pr3+ resulted in the formation of their respective oxide phases as well as perovskites/Ruddlesden–Popper phases. The presence of REE modified the textural and redox properties of the calcined materials. The rare earth element-induced formation of low-temperature reducible MOx species that systematically improved the N2O decomposition on the modified catalysts compared to the pristine M-Al materials by the order of Co &gt; Ni &gt; Cu. The Ce0.5Co0.8Al0.2 catalyst revealed the highest activity and remained stable (approximately 90% of N2O conversion) for 50\ua0h during time-on-stream in 1000\ua0ppm N2O, 200\ua0ppm NO, 20 000\ua0ppm O2, 2500\ua0ppm H2O/N2 balance at WHSV = 16 L g−1\ua0h−1

Geopolymerization of meta-kaolins with different morphologies

The reactivity of two commercial meta-kaolins with similar composition and specific surface areas but different morphologies was tested during geopolymerization with potassium silicate alkaline solution. Manual and short term mechanical stirrings were used to not complete geopolymerization and to emphasize the powders surface reactivity. Moreover, radiation, infra red, micro waves heating were used during curing. The degree of geopolymerization was checked by SEM and N2 adsorption (BET), FTIR and 27Al MAS NMR spectroscopies. The meta-kaolin powder with rounded agglomerates was the less reactive, but it was the more sensitive to the various geopolymerization conditions. The fine dispersed lamellar powder was more reactive and it was mainly affected by mixing. The addition to the potassium silicate alkaline solution of a small alkaline cation such as lithium favoured the dissolution stage during geopolymerization, but decreased the melting temperatur

Trehalose induces autophagy via lysosomal-mediated TFEB activation in models of motoneuron degeneration

Macroautophagy/autophagy, a defense mechanism against aberrant stresses, in neurons counteracts aggregate-prone misfolded protein toxicity. Autophagy induction might be beneficial in neurodegenerative diseases (NDs). The natural compound trehalose promotes autophagy via TFEB (transcription factor EB), ameliorating disease phenotype in multiple ND models, but its mechanism is still obscure. We demonstrated that trehalose regulates autophagy by inducing rapid and transient lysosomal enlargement and membrane permeabilization (LMP). This effect correlated with the calcium-dependent phosphatase PPP3/calcineurin activation, TFEB dephosphorylation and nuclear translocation. Trehalose upregulated genes for the TFEB target and regulator Ppargc1a, lysosomal hydrolases and membrane proteins (Ctsb, Gla, Lamp2a, Mcoln1, Tpp1) and several autophagy-related components (Becn1, Atg10, Atg12, Sqstm1/p62, Map1lc3b, Hspb8 and Bag3) mostly in a PPP3- and TFEB-dependent manner. TFEB silencing counteracted the trehalose pro-degradative activity on misfolded protein causative of motoneuron diseases. Similar effects were exerted by trehalase-resistant trehalose analogs, melibiose and lactulose. Thus, limited lysosomal damage might induce autophagy, perhaps as a compensatory mechanism, a process that is beneficial to counteract neurodegeneration