Copper–aluminum hydrotalcite type precursors for NOx abatement

Synthesis of Reduced Graphene Oxide as a Support for Nano Copper and Palladium/Copper Catalysts for Selective NO Reduction by CO

Copper and palladium/copper nanoparticles supported on reduced graphene oxide catalysts were synthesized and evaluated for the selective NO reduction by CO. The catalysts were characterized by XRD, nitrogen adsorption-desorption, TGA, XPS, TPR, in situ XRD, STEM, and HRTEM. The STEM and HRTEM results showed high metal oxide dispersions on the rGO. XPS results showed the presence of Cu and Pd oxide species. The reduction of copper supported on the rGO occurred in two steps for CuO _x /rGO_c, while that for CuO _x -PdO _y /rGO_c occurred in one step for temperatures lower than 350 °C. Noteworthy is that the in situ XRD results showed that the rGO structure was not affected after reduction at 350 °C. The in situ XRD of reduction revealed the appearance of new phases for copper during the reduction. The catalysts were evaluated in NO reduction by CO. The tests showed that the reduced catalysts presented high performance with NO conversions and N₂ selectivity above 85% at 350 °C.

Optimization of the Washcoat Slurry for Hydrotalcite-Based LNT Catalyst

This work aimed to optimize the washcoat slurry for hydrotalcite-based lean NOx trap (LNT) catalyst. The effects of the slurry properties including pH, solid content, binder and additive on the hydrotalcite-based slurry viscosity were investigated. The particle size distribution of the optimal hydrotalcite-based slurry was measured. A cordierite material was used to coat the optimal slurry, and the washcoat was characterized by X-ray diffraction, scanning electron microscopy and N2 adsorption. The optimal slurry containing Pt and Ba was coated on the cordierite for the preparation of hydrotalcite-based LNT catalyst, and the performances of this catalyst were evaluated by NOx storage test, temperature programmed desorption and NOx reduction. For comparison, the performance of the commercial LNT catalyst with Pt/BaO/Al2O3 was analyzed. After coating, the hydrotalcite-based washcoat was closely contacted with the support, being the main phase MgO and presenting a specific surface area of 86.3 m2/g. The hydrotalcite-based LNT catalyst had better NOx storage and desorption ability, selectivity to N2 and LNT efficiency than the Pt/BaO/Al2O3 catalyst.

Layered Double Hydroxides as Bifunctional Catalysts for the Aryl Borylation under Ligand-Free Conditions

Organic derivatives of boron, such as boronic esters and acids, are important precursors for a wide range of environmental, energy, and health applications. Several catalytic methods for their synthesis have been reported, even though with the use of toxic and structurally complex ligands. Herein, we demonstrate preliminary studies envisaging the synthesis of boronic esters from an inexpensive catalytic system based on Cu/Al layered double hydroxides (LDH) in the presence of Na2PdCl4. The Cu/ Al LDHs were prepared according to coprecipitation method and characterized by X-ray diffraction (XRD) (with Rietveld refinement) to evaluate the contamination with malachite and other phases. Preliminary catalytic results suggest that pure Cu/Al LDH has potential for the borylation of aryl iodides/ bromides in the absence of base. Indeed, a synergic effect between copper and palladium is possibly related to the catalytic efficiency.

The effect of preparation methods on the thermal and chemical reducibility of Cu in Cu-Al oxides

The influence of the preparation methods on the physicochemical properties of Cu and Al oxides was studied. Four different preparation methods were used to synthesize the oxides (catalysts): co-precipitation by the hydrotalcite precursor route (CuAl-HT-c), the solid-state reaction route (CuAl-s), the physical mixing of the oxides (CuAl-o), and individual oxide precipitation followed by physical mixing (CuAl-p). Chemical analysis, X-ray diffraction and textural analysis results of the precursor CuAl-HT-c showed that the respective preparation method is efficient to obtain the hydrotalcite phase with high purity as well as generating a mixed oxide with the greatest surface area among all of the catalysts in this study. The efficacy of this method should be highlighted as it is very difficult to obtain high purity hydrotalcites with copper and aluminum. Furthermore, through the evolution of the FWHM with temperature, this method provided a structurally and texturally more stable mixed oxide. The thermal reducibility of the CuAl-HT-c catalyst was also much higher than that observed in the Cu and Al oxides prepared by other methods. Under an He flow, the CuAl-HT-c catalyst showed a significant reduction of CuO starting at 440 °C, with the formation of Cu2O and metallic Cu, confirmed by XRD and XANES, both in situ. When investigating the effect of the pretreatment gas for this catalyst, H2 reduction occurs faster than with CO, and with less Cu+ formation. Thus, Cu and Al mixed oxides obtained from a precursor with the hydrotalcite structure showed advantages over other methods, presenting unique textural and reducibility properties.