Nano CaCO3 particles in cement mortars towards developing a circular economy in the cement industry

This paper calls into question the effects of incorporating nano calcium carbonate (CaCO3) particles in cement mortars, as they are interesting additive materials already successfully tested as cement nanofiller. These nanoparticles could potentially be prepared through the carbonation route using CO2 from combustion gases from the cement industry. This could enable a circular-economy approach for carbon capture and its re-use within the cement industry, in a sustainable and synergistic manner. In this study, part of the cement content was substituted with commercial nano CaCO3 particles to investigate their effects on the flexural and compressive strength of the resulting cement mortars, after curing for 7 and 28 days. Decreasing the cement content could lead to a reduction in the carbon footprint of cement, which is responsible for approximately 8% of global carbon dioxide emissions. Preliminary results using synthesized CaCO3 particles as nanofillers showed that, after 7 days of curing, mechanical properties of cement mortars improved. This indicates that hydration reaction was accelerated since CaCO3 acts as seeding for this reaction. By contrast, after 28 days of curing, no major improvement was observed. A higher content of calcium carbonate nanoparticles may have reduced the filler effect of these particles due to aggregation phenomena. In the present work, the effects of commercial nano CaCO3 particles on cement hydration were investigated. Mechanical tests showed promising results both after 7 and 28 days of curing. This could lead to the reduction of the carbon footprint of cement manufacturing and produce increasingly better performing building materials. Thus, the development of a circular economy in the cement industry could be achieved

Solid-state ion exchange of Fe in small pore SSZ-13 zeolite: Characterization of the exchanged species and their relevance for the NOx SCR reaction

Solid state ion exchange was performed for the successful introduction of Fe cations in the small pore CHA structured SSZ-13 zeolite. The produced catalysts were characterized by IR and UV-Vis spectroscopies and thermally programmed reaction techniques to probe the Fe sites formed during the exchange and the catalytic activity for the NOx SCR reaction. The results indicate that highly dispersed and heterogeneous Fe sites are formed, and the type depends on the Al distribution in the zeolite. Dimeric Fe species are formed preferentially at the start of the exchange on the 6- and 8-member rings that contain at least two Al exchange sites and once these sites are fully saturated the Fe is exchanged as isolated cations

Evaluation of the mechanical properties of cements with fillers derived from the CO2 reduction of cement plants

This work introduces a novel method for the development of CO2 recovery systems derived from the production process of cement in order to obtain CaCO3 nanofiller in cement-based composites. Research was carried out in collaboration between the Department of Applied Science and Technology (DISAT) and the Department of Structural, Construction and Geotechnical Engineering (DISEG) of Politecnico di Torino. The objective of this method was dual. Firstly, it aimed to obtain a precipitated calcium carbonate - nanoCaCO3 - with a high degree of purity. Secondly, it aimed to optimize the characteristics of these nanoparticles e.g. additional percentages, morphology, particle size distribution or crystal phase, according to their use in cement-based composites. The synthesized nanoCaCO3 particles were subsequently added into the cementitious composites in different percentages according to the weight of the cement, in order to understand their behaviour within the cement matrix. The mechanical properties were also evaluated, both at 7 and 28 days, through three point bending and compression tests. The results of the mechanical tests showed a promising improvement in strength and toughness. This study is a first step towards developing a CO2 circular economy

SO2 deactivation mechanism of NO oxidation and regeneration of the LaCoO3 perovskite

The deactivation mechanism and methods to cope with the poisoning by SO2 of LaCoO3 perovskite-based NO oxidation catalysts were investigated. The LaCoO3 perovskite was synthesized by a sol-gel method and the fresh, sulphate-deactivated and regenerated catalysts were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, H2-and soot-temperature programmed reduction, temperature programmed desorption and diffuse reflectance infrared Fourier transform spectroscopy. The SO2 poisoning strongly affected the NO oxidation activity. It was demonstrated that the deactivation mechanism proceeds in two stages: initially the active sites with a basic character are blocked by SO3 and subsequently the lanthanum sulphate salts grow progressively on the surface and cobalt is unaffected. Above 500 °C, the surface bound sulphates become mobile and migrate into the bulk of the catalyst. Several prevention and regeneration methods were proposed and tested. By mixing the catalyst with Ca(OH)2 as an adsorbent nearly 50% of the original activity was retained. Regeneration by diesel soot was presented here for the first time, where the blocking oxygen can spill over to the soot oxidizing it and releasing the bound sulphur as SO2 and CO2. Furthermore, a facile regeneration method was explored by washing the deactivated catalyst to dissolve the small amounts of sulphates on the surface

Reverse Micelle Strategy for the Synthesis of MnOx-TiO2Active Catalysts for NH3-Selective Catalytic Reduction of NOxat Both Low Temperature and Low Mn Content

MnOx-TiO2catalysts (0, 1, 5, and 10 wt % Mn nominal content) for NH3-SCR (selective catalytic reduction) of NOxhave been synthesized by the reverse micelle-assisted sol-gel procedure, with the aim of improving the dispersion of the active phase, usually poor when obtained by other synthesis methods (e.g., impregnation) and thereby lowering its amount. For comparison, a sample at nominal 10 wt % Mn was obtained by impregnation of the (undoped) TiO2sample. The catalysts were characterized by using an integrated multitechnique approach, encompassing X-ray diffraction followed by Rietveld refinement, micro-Raman spectroscopy, N2isotherm measurement at −196 °C, energy-dispersive X-ray analysis, diffuse reflectance UV-vis spectroscopy, temperature-programmed reduction technique, and X-ray photoelectron spectroscopy. The obtained results prove that the reverse micelle sol-gel approach allowed for enhancing the catalytic activity, in that the catalysts were active in a broad temperature range at a substantially low Mn loading, as compared to the impregnated catalyst. Particularly, the 5 wt % Mn catalyst showed the best NH3-SCR activity in terms of both NOxconversion (ca. 90%) and the amount of produced N2O (ca. 50 ppm) in the 200-250 °C temperature range

Aftertreatment technologies for diesel engines: An overview of the combined systems

The abatement of the pollutants deriving from diesel engines in the vehicle sector still represents an interesting scientific and technological challenge due to increasingly limiting regulations. Meeting the stringent limits of NOx and soot emissions requires a catalytic system with great complexity, size of units, and number of units, as well as increased fuel consumption. Thus, an aftertreatment device for a diesel vehicle requires the use of an integrated catalyst technology for a reduction in the individual emissions of exhaust gas. The representative technologies devoted to the reduction of NOx under lean‐burn operation conditions are selective catalytic reduction (SCR) and the lean NOx trap (LNT), while soot removal is mainly performed by filters (DPF). These devices are normally used in sequence, or a combination of them has been proposed to overcome the drawbacks of the individual devices. This review summarizes the current state of NOx and soot abatement strategies. The main focus of this review is on combined technologies for NOx removal (i.e., LNT–SCR) and for the simultaneous removal of NOx and soot, like SCR‐on‐Filter (SCRoF), in series LNT/DPF and SCR/DPF, and LNT/DPF and SCR/DPF hybrid systems

Effect of inoculum origin and substrate-inoculum ratio to enhance the anaerobic digestion of organic fraction municipal solid waste (OFMSW)

This study evaluated the key role of inoculum in mesophilic anaerobic digestion (AD) of Organic Fraction of Municipal Solid Waste. The effect of two different inocula, the mesophilic digestate of wastewater activated sludge (WAS) and the mesophilic digestate of cow-agriculture sludge (CAS), at three different substrate: inoculum ratios (1:2, 1:1 and 2:1) at three different incubation times (0, 5 and 10 d) were studied in batch feeding reactor for a total of 18 AD configurations. The AD configurations were study through specific biogas and methane productions, first order disintegration kinetics, Gompertz modified study and energy sustainable index. A multi criteria decision aid outranked the 18 AD configurations tested. The study proved that the AD performed with inoculum CAS incubated for 10 d at 2:1 substrate inoculum ratio reached the highest biogas yield and methene content equal to 997.81 NL/kgVS and 70.00% v/v

Soot oxidation in low-O2 and O2-free environments by lanthanum-based perovskites: structural changes and the effect of Ag doping

The use of La-based, Cu (LCO), Mn (LMO) and Fe (LFO) perovskites doped with Ag was studied for potential application as cGPF soot oxidation catalysts. Special emphasis was placed on the effect of the soot, reaction gas composition, changes in rich/lean conditions and the resulting physicochemical changes in the catalyst and their reversibility. The use of a catalyst reduced the soot oxidation temperature significantly in a low-O2 environment and with Ag doping the soot oxidation temperature was decreased by 170 °C in loose contact and 230 °C in tight contact compared to uncatalyzed oxidation. For the soot oxidation in an O2-free environment, the highest oxygen storage capacity was found for LCO and LCAO (1 mol O per molcat). The release of such a high amount of O and reduction of Cu2+ to Cu0 was accompanied by the loss of perovskite structure (LCO → Cu/La2O3), which could be reversed following exposure to a high temperature low-O2 environment