Ternary and quaternary Cr or Ga-containing ex-LDH catalysts—Influence of the additional oxides onto the microstructure and activity of Cu/ZnAl2O4 catalysts

Abstract

The stepwise substitution of Al by Cr and Ga leads to quaternary LDH precursors for Cu/ZnM 2 O 4 (M = Al, Ga, Cr) catalysts. With the substitution of Al by Cr the interaction of the Cu phase with the oxide matrix is gradually weakened, which is caused by the participation of the chromium oxide phase in the redox processes during catalyst preparation. Such reactive Cr oxide matrix is less efficient than the inert Al oxide matrix in stabilizing the special microstructure of Cu/ZnM 2 O 4 catalysts. These weakened interactions led to a lowering of the Cu particle embedment, coinciding with a pronounced Cu crystallite growth during reduction. Both effects partially compensate each other and a maximum in Cu surface area is observed for intermediate Cr contents. In the Ga-substituted catalysts, two distinct Cu species were found for high Ga contents. This is attributed to the presence of partially crystalline spinel and the resulting different strength of interface interaction of the CuO phase with the crystalline and the amorphous oxide. After reduction Cu catalysts with similar average Cu particle sizes as well as Cu surface areas were obtained. In both sample series, the catalytic activity in methanol synthesis does not scale with the Cu surface area and the experiments show that a strong interaction to the oxide is necessary to gain stability and activity of the Cu phase. Al substitution thus confirms that interface interactions between Cu and the oxide seem to beneficially affect the activity of the Cu particles and the optimal catalyst requires a compromise of exposed surface and interface. * Ga20-calc CZA-calc Ga15-calc Ga10-calc Ga5-calc Ga25-calc Ga30-calc Ga33-calc

Synthesis and structural characterization of CuCoFe–layered double hydroxides

“… The roughly equal radius of Cu 2+ (0.73) and Co 2+ (0.70), Cu 2+ could replace a portion of Co 2+ to form CuCoFe-LDH with stable structure, as the dispersive and isolated effect of Co 2+ and Fe 3+ enable Cu 2+ achieving high dispersion in the layer. This is in agreement with Behrens et al, [24] who prepared CuZnAl-LDH successfully.  From XRD analysis, increased crystallinity was obtained by insertion of 60% and 100% copper cations within the CoFe-LDH network.…”

Fluorinated Cu/Zn/Al/Zr hydrotalcites derived nanocatalysts for CO2 hydrogenation to methanol

“…Recently, considerable attention has been focused on hydrotalcite-like compounds (HTlcs) as catalyst precursors, because the nanocatalysts derived from HTlcs possess homogeneous dispersion of metal cations at an atomic level, high stability against sintering, high specific surface area and strongly basic properties [18][19][20]. The general formula of HTlcs is [M 2+ 1Àx M 3+…”

Tailoring of Hydrotalcite-Derived Cu-Based Catalysts for CO2 Hydrogenation to Methanol

“…Therefore, appropriate adsorption amount and adsorption strength of CO 2 are beneficial for the production of methanol, which give a guideline for the design of highly effective and efficient catalysts. On this account, considerable attention was recently paid to hydrotalcite-like compounds (HT) as catalyst precursors, because the catalyst systems derived from hydrotalcite structures possess homogeneous dispersion of metal cations at an atomic level, high stability against sintering, high specific surface area, and strongly basic properties [18][19][20].In the present work, we inspected the catalytic behavior of CuZnAl catalysts as obtained from hydrotalcite-like structures in a CO 2 -to-MeOH hydrogenation reaction. Irrespective of the extent of crystallinity of the coprecipitated phase, the influence of the Cu:Zn:Al ratio on the formation of well-dispersed and active metal particles, generated after calcination and reduction, was addressed.…”

“…Therefore, appropriate adsorption amount and adsorption strength of CO 2 are beneficial for the production of methanol, which give a guideline for the design of highly effective and efficient catalysts. On this account, considerable attention was recently paid to hydrotalcite-like compounds (HT) as catalyst precursors, because the catalyst systems derived from hydrotalcite structures possess homogeneous dispersion of metal cations at an atomic level, high stability against sintering, high specific surface area, and strongly basic properties [18][19][20].…”