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. 2023 Jul 14;13(15):9946-9959.
doi: 10.1021/acscatal.3c02534. eCollection 2023 Aug 4.

ZrO2-Promoted Cu-Co, Cu-Fe and Co-Fe Catalysts for Higher Alcohol Synthesis

Yuzhen Ge  1 , Tangsheng Zou  1 , Antonio J Martín  1 , Javier Pérez-Ramírez  1
Affiliations

ZrO2-Promoted Cu-Co, Cu-Fe and Co-Fe Catalysts for Higher Alcohol Synthesis

Yuzhen Ge et al. ACS Catal. .

Abstract

The development of efficient catalysts for the direct synthesis of higher alcohols (HA) via CO hydrogenation has remained a prominent research challenge. While modified Fischer-Tropsch synthesis (m-FTS) systems hold great potential, they often retain limited active site density under operating conditions for industrially relevant performance. Aimed at improving existing catalyst architectures, this study investigates the impact of highly dispersed metal oxides of Co-Cu, Cu-Fe, and Co-Fe m-FTS systems and demonstrates the viability of ZrO2 as a general promoter in the direct synthesis of HA from syngas. A volcano-like composition-performance relationship, in which 5-10 mol % ZrO2 resulted in maximal HA productivity, governs all catalyst families. The promotional effect resulted in a 2.5-fold increase in HA productivity for the optimized Cu1Co4@ZrO2-5 catalyst (Cu:Co = 1:4, 5 mol % ZrO2) compared to its ZrO2-free counterpart and placed Co1Fe4@ZrO2-10 among the most productive systems (345 mgHA h-1 gcat-1) reported in this category under comparable operating conditions, with stable performance for at least 300 h. ZrO2 assumes an amorphous and defective nature on the catalysts, leading to enhanced H2 and CO activation, facilitated formation of metallic and carbide phases, and structural stabilization.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Catalyst architectures for bimetallic M1M2 catalysts containing a variable fraction of a metal oxide (MOx) of either zero, a small, or the largest fraction. α:β represents the molar M1:M2 ratio and γ the molar content of metal oxide.
Figure 2
Figure 2
Sol–gel synthesis procedure developed for M1αM2β@MOx-γ catalysts. Synthesis steps are detailed in the Experimental Section.
Figure 3
Figure 3
(a) Influence of the α:β ratio on catalytic performance for CuαCoβ catalysts. Reaction conditions: T = 543 K, P = 5.0 MPa, and H2:CO = 2.0. GHSV = 12000 cm3 h–1 gcat–1. Influence of MOx on (b) catalytic performance, (c) the relation between STYHA and SBET, and (d) STYHA normalized by SBET (rHA) for Cu1Co4@MOx-10 catalysts. Reaction conditions: T = 543 K, P = 5.0 MPa, H2:CO = 2.0, GHSV = 24000 cm3 h–1 gcat–1. Error bars representing the standard deviation of 3 measurements at TOS between 14 and 16 h are shown. Trend lines are added to guide the eye.
Figure 4
Figure 4
Influence of γ on (a) catalytic performance and (b) SBET and crystallite sizes as determined by XRD analysis for Cu1Co4@ZrO2-γ catalysts. Systems with γ = 0 mol % and γ = 90 mol % are equivalent to Cu1Co4 and supported Cu1Co4/ZrO2-90 systems, respectively. Influence of the α/β ratio on (c) catalytic performance and (d) alcohol distribution for CuαCoβ@ZrO2-5 catalysts. Reaction conditions: T = 543 K, P = 5.0 MPa, H2:CO = 2.0, GHSV = 24000 cm3 h–1 gcat–1. Error bars representing the standard deviation of 3 measurements at TOS between 14 and 16 h are shown. Trend lines are added to guide the eye.
Figure 5
Figure 5
Influence of (a) temperature, (b) pressure, (c) space velocity, and (d) H2:CO ratio on catalytic performance for the Cu1Co4@ZrO2-5 catalyst. Reaction conditions: T = 543 K, P = 5.0 MPa, H2:CO = 2, GHSV = 24000 cm3 h–1 gcat–1. Error bars representing the standard deviation of 3 measurements at TOS between 14 and 16 h are shown. (e) Stability test over Cu1Co4@ZrO2-5. Reaction conditions: T = 548 K, P = 5.5 MPa, H2:CO = 1.5, GHSV = 36000 cm3 h–1 gcat–1. Trend lines are added to guide the eye.
Figure 6
Figure 6
Influence of γ on catalytic performance for (a) Cu1Fe2@ZrO2-γ and (b) Co1Fe4@ZrO2-γ. Reaction conditions: T = 523 K, P = 5.0 MPa, H2:CO = 2.0, GHSV = 24000 cm3 h–1 gcat–1. Error bars representing the standard deviation of 3 measurements at TOS between 14 and 16 h are shown. Trend lines are added to guide the eye.
Figure 7
Figure 7
(a) Influence of ZrO2 content on normalized STYHA for M1M2@ZrO2 catalysts. (b) Comparison of STYHA and SHA of M1M2@ZrO2 catalysts at individually optimized reaction conditions with those of representative m-FTS catalysts previously reported in the literature (Table S17). (1) Co1Fe4@ZrO2-10, reaction conditions: T = 518 K, P = 5.5 MPa, H2:CO = 1.5, and GHSV = 48000 cm3 h–1 gcat–1. (2) Cu1Fe2@ZrO2-10, reaction conditions: T = 503 K, P = 5.5 MPa, H2:CO = 1.5, GHSV = 36000 cm3 h–1 gcat–1. (3) Cu1Co4@ZrO2-5, reaction conditions: T = 548 K, P = 5.5 MPa, H2:CO = 1.5, GHSV = 36000 cm3 h–1 gcat–1. (4) Co1Fe4@ZrO2-10, reaction conditions: T = 473 K, P = 5.0 MPa, H2:CO = 2.0, GHSV = 24000 cm3 h–1 gcat–1.
Figure 8
Figure 8
STEM-EDX elemental mapping and TEM images after reaction obtained from catalysts with α:β = 1:4 with varying ZrO2 contents: (a) Cu1Co4, (b) ZrO2-promoted Cu1Co4@ZrO2-5, and (c) supported Cu1Co4/ZrO2-90. Scale bars represent 50 nm for elemental maps and 20 nm for TEM images.
Figure 9
Figure 9
Influence of γ on the response to H2-TPR analysis for Cu1Co4@ZrO2-γ catalysts. Signals used to deconvolute experimental profiles correspond to the reduction of (a) Cu oxide; (b) Co oxides; and (c) additional Cu-Co-ZrO2 oxidic phases. (d) Influence of γ on the phase reduction peak temperature, Tpeak.
Figure 10
Figure 10
Temperature-programmed H2-D2 exchange profiles for (a) Cu1Co4 and (b) Cu1Co4@ZrO2-10, with the exchange temperature (at the onset of HD formation) marked.
Figure 11
Figure 11
XPS spectra around indicated regions after reaction obtained from catalysts with α:β = 1:4 with varying ZrO2 contents: (a) Cu1Co4, (b) ZrO2-promoted Cu1Co4@ZrO2-5, and (c) supported Cu1Co4/ZrO2-90. Signals used to deconvolute experimental spectra correspond to indicated species.
Figure 12
Figure 12
STEM-EDX elemental mapping and STEM images of (a) Cu1Fe2@ZrO2-10 and (b) Co1Fe4@ZrO2-10. Scale bars represent 50 nm in all images.
Figure 13
Figure 13
XPS spectra of used Cu1Fe2@ZrO2-10 (above) and Co1Fe4@ZrO2-10 samples (below) for (a) C 1s, (b) O 1s and (c) Zr 3d regions. Signals used to deconvolute experimental spectra correspond to indicated species. Influence of ZrO2 content on the phase reduction peak temperature (Tpeak) of (d) Cu1Fe2@ZrO2-10 and (e) Co1Fe4@ZrO2-10. The values of Tpeak were extracted from the H2-TPR results in Figures S25 and S26.
Figure 14
Figure 14
Overview of structural and catalytic features characteristic of zirconia-containing M1M2 catalysts for the analyzed architectures.
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