Performance Improvement of Nanocatalysts by Promoter-Induced Defects in the Support Material: Methanol Synthesis over Cu/ZnO:Al

Abstract

Addition of small amounts of promoters to solid catalysts can cause pronounced improvement in the catalytic properties. For the complex catalysts employed in industrial processes, the fate and mode of operation of promoters is often not well understood, which hinders a more rational optimization of these important materials. Herein we show for the example of the industrial Cu/ZnO/Al2O3 catalyst for methanol synthesis how structure-performance relationships can deliver such insights and shed light on the role of the Al promoter in this system. We were able to discriminate a structural effect and an electronic promoting effect, identify the relevant Al species as a dopant in ZnO, and determine the optimal Al content of improved Cu/ZnO:Al catalysts. By analogy to Ga- and Cr-promoted samples, we conclude that there is a general effect of promoter-induced defects in ZnO on the metal-support interactions and propose the relevance of this promotion mechanism for other metal/oxide catalysts also.

High-Pressure Pulsing of Ammonia Results in Carbamate as Strongly Inhibiting Adsorbate of Methanol Synthesis over Cu/ZnO/Al2O3

“…The composition (Figure S1 and Table S1), the XRD patterns of the precursor (Figure S2) and that of the calcined form (Figure S3), the N 2 adsorption isotherms (Figure S4 and Table S2), the TPR curve (Figure S5a), and the N 2 O-RFC profile (Figure S5b) of the CZA catalyst are presented in the Supporting Information. In agreement with previous results, XRD confirmed that the precursor of the catalyst mainly crystallized in a malachite structure (Figure S2) and that the typical by-phase of Al-rich hydrotalcite is hardly observed but cannot be completely ruled out based on the powder patterns. The shift of the 201̅ peak corresponds to a d -spacing of 2.754 Å and is in line with the results obtained by Schumann et al This value indicates a proper substitution of Cu 2+ by Zn 2+ and Al 3+ cations.…”

High-Pressure Pulsing of Ammonia Results in Carbamate as Strongly Inhibiting Adsorbate of Methanol Synthesis over Cu/ZnO/Al2O3

“…The composition (Figure S1 and Table S1), the XRD patterns of the precursor (Figure S2) and that of the calcined form (Figure S3), the N 2 adsorption isotherms (Figure S4 and Table S2), the TPR curve (Figure S5a), and the N 2 O-RFC profile (Figure S5b) of the CZA catalyst are presented in the Supporting Information. In agreement with previous results, XRD confirmed that the precursor of the catalyst mainly crystallized in a malachite structure (Figure S2) and that the typical by-phase of Al-rich hydrotalcite is hardly observed but cannot be completely ruled out based on the powder patterns. The shift of the 201̅ peak corresponds to a d -spacing of 2.754 Å and is in line with the results obtained by Schumann et al This value indicates a proper substitution of Cu 2+ by Zn 2+ and Al 3+ cations.…”

Isomorphous substitution method to fabricating pure phase Al‐doped zinc malachite: defects driven promotion improvement and enhanced synergy between Cu−ZnO

“…This is mainly due to the additional charge introduced by Al 3+ in the malachite structure. The possible ways of charge balance may include generation of cation or proton vacancies in the lattice [12] . The formation of Al‐rich by‐phase with excess Al 3+ concentration is in good agreement with the previous report [14] .…”

“…The possible ways of charge balance may include generation of cation or proton vacancies in the lattice. [12] The formation of Al-rich by-phase with excess Al 3 + concentration is in good agreement with the previous report. [14] This indicates that the maximum concentration of Al 3 + that can be accommodated by malachite structure is Al/(Al + Cu) = 0.08.…”

Highly active Cu/ZnO–Al catalyst for methanol synthesis: effect of aging on its structure and activity

“…The contribution of ZnO x species to the values of Cu surface area of Cu/ZnO–Al-100 and Cu/ZnO–Al-100-160 catalysts cannot be discarded because they are promoted by the possible insertion of Al 3+ ions into ZnO strongly favoured in the compositional window Al/Cu/Zn used in this work. 16 It should be noted that the Cu/ZnO–Al-100 and Cu/ZnO–Al-160 catalysts exhibited very high specific Cu surface areas which agreed well with other published data for highly active CH 3 OH synthesis catalysts. 19 …”

“…6,22 Diffraction peaks corresponding to additional phases such as hydrotalcite or aurichalcite were not observed in any of the CZA precursors. This is in agreement with results found by Behrens et al 16 who found that low amounts of Al facilitated the incorporation of Zn into the malachite structure, thus inhibiting the formation of crystalline Znrich by-product phases. Only in the precipitate examined close to the crystallization point (CZA-70, Fig.…”

High-Pressure Pulsing of Ammonia Results in Carbamate as Strongly Inhibiting Adsorbate of Methanol Synthesis over Cu/ZnO/Al2O3

“…The composition (Figure S1 and Table S1), the XRD patterns of the precursor (Figure S2) and that of the calcined form (Figure S3), the N 2 adsorption isotherms (Figure S4 and Table S2), the TPR curve (Figure S5a), and the N 2 O-RFC profile (Figure S5b) of the CZA catalyst are presented in the Supporting Information. In agreement with previous results, XRD confirmed that the precursor of the catalyst mainly crystallized in a malachite structure (Figure S2) and that the typical by-phase of Al-rich hydrotalcite is hardly observed but cannot be completely ruled out based on the powder patterns. The shift of the 201̅ peak corresponds to a d -spacing of 2.754 Å and is in line with the results obtained by Schumann et al This value indicates a proper substitution of Cu 2+ by Zn 2+ and Al 3+ cations.…”

Isomorphous substitution method to fabricating pure phase Al‐doped zinc malachite: defects driven promotion improvement and enhanced synergy between Cu−ZnO

“…This is mainly due to the additional charge introduced by Al 3+ in the malachite structure. The possible ways of charge balance may include generation of cation or proton vacancies in the lattice [12] . The formation of Al‐rich by‐phase with excess Al 3+ concentration is in good agreement with the previous report [14] .…”

“…The possible ways of charge balance may include generation of cation or proton vacancies in the lattice. [12] The formation of Al-rich by-phase with excess Al 3 + concentration is in good agreement with the previous report. [14] This indicates that the maximum concentration of Al 3 + that can be accommodated by malachite structure is Al/(Al + Cu) = 0.08.…”

Highly active Cu/ZnO–Al catalyst for methanol synthesis: effect of aging on its structure and activity

“…The contribution of ZnO x species to the values of Cu surface area of Cu/ZnO–Al-100 and Cu/ZnO–Al-100-160 catalysts cannot be discarded because they are promoted by the possible insertion of Al 3+ ions into ZnO strongly favoured in the compositional window Al/Cu/Zn used in this work. 16 It should be noted that the Cu/ZnO–Al-100 and Cu/ZnO–Al-160 catalysts exhibited very high specific Cu surface areas which agreed well with other published data for highly active CH 3 OH synthesis catalysts. 19 …”

“…6,22 Diffraction peaks corresponding to additional phases such as hydrotalcite or aurichalcite were not observed in any of the CZA precursors. This is in agreement with results found by Behrens et al 16 who found that low amounts of Al facilitated the incorporation of Zn into the malachite structure, thus inhibiting the formation of crystalline Znrich by-product phases. Only in the precipitate examined close to the crystallization point (CZA-70, Fig.…”

High-Pressure Pulsing of Ammonia Results in Carbamate as Strongly Inhibiting Adsorbate of Methanol Synthesis over Cu/ZnO/Al2O3

“…The composition (Figure S1 and Table S1), the XRD patterns of the precursor (Figure S2) and that of the calcined form (Figure S3), the N 2 adsorption isotherms (Figure S4 and Table S2), the TPR curve (Figure S5a), and the N 2 O-RFC profile (Figure S5b) of the CZA catalyst are presented in the Supporting Information. In agreement with previous results, XRD confirmed that the precursor of the catalyst mainly crystallized in a malachite structure (Figure S2) and that the typical by-phase of Al-rich hydrotalcite is hardly observed but cannot be completely ruled out based on the powder patterns. The shift of the 201̅ peak corresponds to a d -spacing of 2.754 Å and is in line with the results obtained by Schumann et al This value indicates a proper substitution of Cu 2+ by Zn 2+ and Al 3+ cations.…”

Isomorphous substitution method to fabricating pure phase Al‐doped zinc malachite: defects driven promotion improvement and enhanced synergy between Cu−ZnO

“…This is mainly due to the additional charge introduced by Al 3+ in the malachite structure. The possible ways of charge balance may include generation of cation or proton vacancies in the lattice [12] . The formation of Al‐rich by‐phase with excess Al 3+ concentration is in good agreement with the previous report [14] .…”

“…The possible ways of charge balance may include generation of cation or proton vacancies in the lattice. [12] The formation of Al-rich by-phase with excess Al 3 + concentration is in good agreement with the previous report. [14] This indicates that the maximum concentration of Al 3 + that can be accommodated by malachite structure is Al/(Al + Cu) = 0.08.…”

Highly active Cu/ZnO–Al catalyst for methanol synthesis: effect of aging on its structure and activity

“…The contribution of ZnO x species to the values of Cu surface area of Cu/ZnO–Al-100 and Cu/ZnO–Al-100-160 catalysts cannot be discarded because they are promoted by the possible insertion of Al 3+ ions into ZnO strongly favoured in the compositional window Al/Cu/Zn used in this work. 16 It should be noted that the Cu/ZnO–Al-100 and Cu/ZnO–Al-160 catalysts exhibited very high specific Cu surface areas which agreed well with other published data for highly active CH 3 OH synthesis catalysts. 19 …”

“…6,22 Diffraction peaks corresponding to additional phases such as hydrotalcite or aurichalcite were not observed in any of the CZA precursors. This is in agreement with results found by Behrens et al 16 who found that low amounts of Al facilitated the incorporation of Zn into the malachite structure, thus inhibiting the formation of crystalline Znrich by-product phases. Only in the precipitate examined close to the crystallization point (CZA-70, Fig.…”