Comparison of CuxZnAlO mixed oxide catalysts derived from multicationic and hybrid LDH precursors for methane total oxidation

Răciulete, Monica; Layrac, Géraldine; Tichit, Didier; Marcu, Ioan–Cezar

doi:10.1016/j.apcata.2014.03.018

Cited by 35 publications

(12 citation statements)

References 48 publications

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“…Recently, Cu-based catalysts obtained from LDH precursors were investigated in CO 2 hydrogenation [11,12] as well as low temperature shift reactions [13] and methanol oxidation [14]. In a previous study [15] we presented a Cu-based catalyst with a high intrinsic activity in methanol synthesis obtained from Cu,Zn,Al LDH precursors.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2015

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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

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Section: Introductionmentioning

confidence: 99%

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

et al. 2015

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“…Several studies of synthesis of very useful multicationic Cu-containing LDH as catalyst precursors have indeed confirmed that pure crystallographic LDH phases were obtained in wide ranges of M 2+ /M 3+ atomic ratios with M 2+ = Cu 2+ , Ni 2+ , Co 2+ , Zn 2+ , Mg 2+ and M 3+ = Al 3+ and/or Fe 3+ , and at varying co-precipitation pHs. Marchi et al, 2003;Trujillano et al, 2005;Raciulete et al, 2014;Li et al, 2015;Zhang et al, 2017;Lucarelli et al, 2018;Said et al, 2018;Lu et al, 2019) That confirms the versatility of copper to form LDH phases in systems combining several divalent and/or trivalent cations and suggests that the Jahn-Teller effect in Cu-Al LDH was cleverly overpassed by separating Cu cations in the brucite-like layers of multicationic LDH. Then, in addition to insights into the mechanism of formation, a relevant objective of the present work was to obtain pure Cu-Al LDH phase through the direct colloidal synthesis route from HPIC micelles.…”

Section: Introductionmentioning

confidence: 64%

Comprehensive study of the formation of stable colloids of Cu Al layered double hydroxide assisted by double hydrophilic block copolymers

Layrac

Harrisson

Destarac

et al. 2020

Applied Clay Science

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The formation of stable aqueous colloidal suspensions of Cu-Al layered double hydroxide (LDH) assisted by double-hydrophilic block copolymers was investigated. It was of utmost importance since the direct preparation LDH colloids of controlled size is still a major challenge ; moreover, regarding the Cu-Al system, the mechanism of formation of the LDH phase is not well understood yet. Cu-Al LDH nanoparticles were obtained by complexing Cu 2+ and Al 3+ cation mixture (Cu 2+ /Al 3+ = 2) with an asymmetric poly(acrylamide)-b-poly(acrylic acid) block copolymer, followed by metal cation hydroxylation. The mechanism of formation of the Cu-Al LDH was studied and compared to that of Mg-Al LDH. ICP-MS analysis of the hybrid polyion complex (HPIC) micelles obtained at increasing complexation ratio, i. e. the ratio of the molar concentration of complexing acrylate group of DHBC to M 2+ and Al 3+ cations (R = AA/(M 2+ + Al 3+)), showed higher selectivity of DHBC toward Al 3+ and, among M 2+ cations, for Cu 2+ than for Mg 2+. Hydroxylation of the HPIC micelles led to macroscopic precipitates at R values below flocculation thresholds, ie. R1 = 0.43 for DHBC/Cu-Al and 0.13 for and DHBC/Mg-Al suspensions, while stable suspensions were formed above R1. The hydrodynamic diameter (Dh) of the colloids determined by DLS decreased from 160 to 50 nm and from 350 to 50 nm in the DHBC/Cu-Al and DHBC/Mg-Al colloids, respectively, when R increased from R1 to 1. XRD and TEM analyses of the dried colloidal suspensions (R > R1) revealed the presence of Cu-Al LDH and Mg-Al LDH phases and elemental analyses confirmed that M(II)/Al = 2. Particle sizes were lower in Cu-Al LDH than in Mg-Al LDH. Titration curves corresponding to progressive hydroxylation of DHBC/Cu(or Mg)-Al solutions at fixed complexation ratio R allowed establishing that formation of Cu-Al and Mg-Al LDH obeyed to a similar sequential mechanism in two steps but involving different aluminum hydroxide precursors according to the different pH values of precipitation. Cu-Al LDH was obtained by combination of aluminum poly(hydr)oxide species with dissolved copper-based species at pH ~ 5.5, while Mg-Al LDH resulted from combination of Al(OH)3 and dissolved Mg 2+ at pH ~ 8.

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“…1) of the reference MgAl-LDH sample shows typical pattern of hydrotalcite-like materials, with diffraction lines indexed on a hexagonal unit cell with the space group R-3 m [27]. The sharp and symmetric diffraction lines at 2 of 11.4, 22.8 and 34.6 • , assigned to (003), (006) and (009) planes [28], indicate a well-formed crystalline layered structure. The basal spacing distance d 003 , determined from the position of the (003) reflection is 7.77 Å and corresponds to carbonate as compensating anion.…”

Section: Resultsmentioning

confidence: 99%

Levulinate-intercalated LDH: A potential heterogeneous organocatalyst for the green epoxidation of α,β-unsaturated esters

et al. 2018

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Comparison of CuxZnAlO mixed oxide catalysts derived from multicationic and hybrid LDH precursors for methane total oxidation

Cited by 35 publications

References 48 publications

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

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

Comprehensive study of the formation of stable colloids of Cu Al layered double hydroxide assisted by double hydrophilic block copolymers

Levulinate-intercalated LDH: A potential heterogeneous organocatalyst for the green epoxidation of α,β-unsaturated esters

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