Next Article in Journal
Preparation of Recyclable Magnetic Catalyst (Pd/PDA@Fe3O4) and the Catalytic Degradation of 4-Nitrophenol and Rhodamine B
Next Article in Special Issue
Design of Multicatalytic Systems Through Self-Assembly
Previous Article in Journal
Zeolite-Supported TiO2 for Enhanced Photocatalytic Performance in Environmental Applications: A Review
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Catalysts
Volume 15
Issue 2
10.3390/catal15020176
catalysts-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Promoting Effect of Copper Doping on LaMO3 (M = Mn, Fe, Co, Ni) Perovskite-Supported Gold Catalysts for Selective Gas-Phase Ethanol Oxidation

by
Lijun Yue
,
Jie Wang
and
Peng Liu
*
Key Laboratory of Material Chemistry for Energy Conversion and Storage (Ministry of Education), Hubei Key Laboratory of Material Chemistry and Service Failure, School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, Wuhan 430074, China
*
Author to whom correspondence should be addressed.
Catalysts 2025, 15(2), 176; https://doi.org/10.3390/catal15020176
Submission received: 11 January 2025 / Revised: 7 February 2025 / Accepted: 11 February 2025 / Published: 13 February 2025
(This article belongs to the Special Issue New Insights into Synergistic Dual Catalysis)
Browse Figures
Versions Notes

Abstract

:
Developing more effective gold–support synergy is essential for enhancing the catalytic performance of supported gold nanoparticles (AuNPs) in the gas-phase oxidation of ethanol to acetaldehyde (AC) at lower temperatures. This study demonstrates a significantly improved Au–support synergy achieved by copper doping in LaMO3 (M = Mn, Fe, Co, Ni) perovskites. Among the various Au/LaMCuO3 catalysts, Au/LaMnCuO3 exhibited exceptional catalytic activity, achieving an AC yield of up to 91% and the highest space-time yield of 764 gAC gAu−1 h−1 at 225 °C. Notably, this catalyst showed excellent hydrothermal stability, maintaining performance for at least 100 h without significant deactivation when fed with 50% aqueous ethanol. Comprehensive characterization reveals that Cu doping facilitates the formation of surface oxygen vacancies on the Au/LaMCuO3 catalysts and enhances Au–support interactions. The LaMnCuO3 perovskite stabilizes the crucial Cu+ species, resulting in a stable Au-Mn-Cu synergy within the Au/LaMnCuO3 catalyst, which facilitates the activation of O2 and ethanol at lower temperatures. The optimization of the reaction conditions further improves AC productivity. Kinetic studies indicate that the cleavages of both the O-H bond and the α-C-H bond of ethanol are the rate-controlling steps.

1. Introduction

Biomass is widely recognized as a renewable, zero-carbon energy source, capable of producing nearly 100 billion liters of bioethanol annually through fermentation [1]. As a versatile platform molecule, bioethanol facilitates the sustainable production of value-added chemicals, including acetaldehyde (AC), butanol, and butadiene [2,3,4]. Among these, AC is a crucial intermediate in various chemical processes. The selective oxidation of bioethanol to AC presents a greener alternative to the conventional ethylene-based Wacker oxidation, aligning with sustainable development goals [5]. However, achieving high AC yield remains challenging due to the reactive nature of both ethanol and AC under typical reaction conditions. Therefore, developing a catalyst that can achieve high ethanol conversion and AC selectivity at relatively low temperatures (<250 °C) is essential for promoting the practical production of AC from bioethanol.
Ethanol gas-phase oxidation catalysts are generally classified into two main categories: non-precious metal catalysts (including transition metal oxides and carbon-based materials) and precious metal catalysts. Transition metal (such as V, Mn, Co, Cu, and Mo) oxides are abundant and cost-effective; however, they are difficult to achieve high AC yield (>80%) below 250 °C [6,7,8,9]. Although carbon-based catalysts offer adjustable structures, their performance in low-temperature oxidation is limited [10,11]. In contrast, supported precious metal catalysts, such as Pd, Pt, and Au, exhibit high catalytic activity at lower temperatures [12,13,14,15,16]. Notably, gold is particularly effective at activating the α-C-H bond of ethanol compared to Pt and Pd. Additionally, AC is only weakly adsorbed on Au, allowing it to desorb more readily instead of undergoing further dehydrogenation [17]. However, challenges such as Ostwald ripening, particle migration, and agglomeration can lead to the sintering and deactivation of supported Au nanoparticles (AuNPs) [18].
The choice of support material is crucial for stabilizing AuNPs and facilitating the activation of ethanol and oxygen [19]. Recent studies have demonstrated that the nature of support significantly impacts product selectivity. For example, Au supported on acidic or basic oxides primarily yields AC, while p-type semiconductor oxides favor complete oxidation to CO2 [20]. Liu et al. [21] developed a Au/MgCuCr2O4 catalyst that achieved 95% AC selectivity and 100% ethanol conversion at 250 °C, illustrating the synergistic effect between Au0 and Cu⁺ species in enhancing the activation of O2 and ethanol, thereby promoting AC production [22]. Similarly, Chen et al. [23] reported that the Au/CuSiO3 catalyst exhibited a comparable Au-Cu synergistic effect, achieving an AC yield of approximately 91% at 250 °C. Despite these advancements, the pursuit of more efficient and non-toxic Au-based catalysts remains a significant challenge.
Perovskite oxides with the general formula ABO3, where A represents a rare-earth or alkaline metal and B denotes a transition metal, have been widely studied in catalysis [24,25,26]. In this structure, the A sites provide stability, while the B sites contribute to catalytic activity [27]. Lanthanum-based perovskites, namely, LaBO3, are recognized as promising catalytic materials due to their easy preparation and high thermal stability [24]. The incorporation of Cu dopants into the LaBO3 structure has been shown to enhance reducibility and oxygen mobility [28,29,30]. However, the use of Au-loaded perovskites for selective ethanol oxidation remains unexplored. To address this research gap, this study investigates the synergistic interaction between AuNPs and perovskite oxide supports. A series of Au/LaMO3 and Au/LaMCuO3 (M = Mn, Fe, Co, Ni) catalysts were synthesized and evaluated for gas-phase ethanol oxidation to determine whether a novel Au-M or Au-Cu-M synergy occurs. The structure–performance relationships of these catalysts were investigated, highlighting the promoting effect of copper doping on the catalytic activity. Additionally, a series of kinetic experiments were performed to understand the underlying reaction mechanisms, revealing that the activations of both O-H and α-C-H bonds of ethanol are rate-limiting steps in the gas-phase ethanol reaction process. This work provides valuable insights into multi-metal synergistic catalysis and paves the way for the design of efficient, environmentally friendly Au-based catalysts.

2. Results and Discussion

2.1. Characterization of Catalyst

Figure 1and Figure S1 show the X-ray diffraction (XRD) patterns of various perovskite-supported Au catalysts and their corresponding perovskite supports, respectively. The LaMO3 and Cu-doped LaMO3 (M = Mn, Fe, Co, and Ni) samples demonstrate typical perovskite structures, with reference patterns from JCPDS: LaMnO3 (#89-8775), LaFeO3 (#74-2203), LaCoO3 (#48-0123), and LaNiO3 (#79-2448). Although Cu doping and Au loading did not affect the structural integrity of the perovskite supports, they did exert some influence on the lattice parameters, as shown in Table S1. The symmetrical (110) and (104) planes of LaMnO3 and LaNiO3 transformed into asymmetrical planes following Cu doping (see Figure S1). The diffraction peak corresponding to the Au (111) plane at 2θ = 38.2° is minimal in all Au-loaded samples, indicating a fine dispersion of AuNPs. This conclusion is corroborated by the transmission electron microscopy (TEM) images presented in Figure 2, which reveal small AuNP sizes ranging from 2 to 6 nm and a uniform distribution across the catalyst surfaces. The average AuNP sizes, gold loadings, and specific surface areas of the gold catalysts are summarized in Table 1. The incorporation of Cu into the LaMO3 supports led to a reduction in surface area from 4–7 m2/g to 2–5 m2/g and an increase in the average AuNP size from 2–3 nm to 3–6 nm. Notably, the decreased surface area of LaMCuO3 following Cu doping caused the significant aggregation of AuNPs (>6 nm) at a high Au loading of 1.0 wt%. Therefore, a targeted Au loading of 0.5 wt% was selected for Au/LaMCuO3.
X-ray photoelectron spectroscopy (XPS) was employed to reveal the surface chemical states of Au, Cu, M, and O of the Au/LaMCuO3 catalysts. The Au 4f, Cu 2p, and O 1s XPS spectra are shown in Figure 3, while the M 2p XPS spectra are presented in Figure S2. The Au 4f7/2 binding energy (BE) of ~84.0 eV observed in the Au/LaMnCuO3 catalyst is indicative of metallic Au0 [21]. In contrast, the lower Au 4f7/2 BE of ~83.7–83.9 eV observed in the Au/LaFeCuO3, Au/LaCoCuO3, and Au/LaNiCuO3 catalysts indicates the presence of negatively charged Auδ− species, which implies charge transfer from the perovskite supports to the AuNPs [31,32]. In the Cu 2p3/2 spectra, Cu+ and Cu2+ species are detected at ~932.0 and 934.0 eV, respectively, along with shakeup features for Cu2+ in the range of 938–946 eV [22,33]. Notably, Cu⁺ is identified in the Au/LaMnCuO3 and Au/LaFeCuO3 catalysts, while other Au/LaMCuO3 catalysts contain only Cu2⁺ species. From the M 2p3/2 spectra, Mn4+ (643.7 eV)/Mn3+ (641.8 eV)/Mn2+ (640.9 eV) [34,35], Fe3+ (712.5 eV)/Fe2+ (709.9 eV) [36,37], and Co3+ (779.6 eV)/Co2+ (781.0 eV) [38] species were also identified. The satisfactory deconvolution of the Ni 2p signal cannot be achieved due to the overlap with the La 3d signal [39]. The surface molar ratios of M/Cu for the Au/LaMCuO3 (M = Mn, Fe, and Co) catalysts were calculated as 3.5, 2.3, and 6.8, respectively. Given the theoretical M/Cu ratio of 3.0, the Co and Cu species are, respectively, more abundant on the surface of Au/LaCoCuO3 and Au/LaFeCuO3 compared to the other catalysts. In the O 1s spectra, four distinct surface oxygen species were identified at ~529.0, 530.5, 531.7, and 533.0 eV, corresponding to lattice oxygen (OL), oxygen vacancies (OV), hydroxyl groups or adsorbed oxygen (OA), and surface adsorbed water (OW), respectively [40,41]. Although the fraction of OV remained ~20%, the fraction of OL and OA varied on a large scale (16–58%). The (OV + OA)/OL ratio increased in the following order: Au/LaNiCuO3 (0.7) < Au/LaMnCuO3 (1.0) < Au/LaCoCuO3 (1.2) < Au/LaFeCuO3 (1.3). Importantly, Au/LaMnO3 and Au/LaFeO3 displayed a significantly lower (OV + OA)/OL ratio (~0.5) than the corresponding Au/LaMnCuO3 and Au/LaFeCuO3 catalysts (Figure S2). These findings suggest that doping Cu into the LaMO3 perovskite structure enhances the generation of oxygen vacancies.
Temperature-programmed reduction with H2 (H2-TPR) was employed to study the reducibility of the perovskites and their corresponding gold catalysts. The H2-TPR profiles are presented in Figure 4, while the amounts of H2 consumption are summarized in Table 1. For LaMnO3, the initial reduction peak at 450 °C corresponds to the reduction of surface Mn4+/Mn3+ to Mn3+/Mn2+ and the removal of surface-adsorbed oxygen species [39,41]. The subsequent peak at 800 °C is attributed to the reduction of bulk Mn3+ to Mn2+. In contrast, the reduction peaks observed for LaFeO3 are relatively minor due to the low reducibility of iron species within the LaFeO3 structure below 800 °C, as reported in previous studies [42,43]. The reduction behavior of LaCoO3 and LaNiO3 aligns with earlier studies [39,44], where the reduction of Co3+ to Co2+ and Ni3+ to Ni2+ occurs at ~400 °C, followed by the reduction of Co2+ and Ni2+ to metallic Co0 and Ni0 at around 550 °C. Upon Cu doping, the starting reduction temperature of LaMCuO3 shifted to lower temperatures, accompanied by an increase in H2 uptake compared to the undoped counterparts. LaFeCuO3 displayed a significantly enhanced reduction peak at 330 °C, attributed to the reduction of Cu2+/Cu+ to Cu0. The isomorphous substitution of M by Cu in the LaMCuO3 (M = Mn, Co, and Ni) structure contributes to this increased H2 uptake, which is associated with the formation of additional surface oxygen vacancies and adsorbed oxygen species. Interestingly, the first reduction peak of LaMnCuO3 did not shift to lower temperature but increased to 500 °C, indicating a special stabilization effect of the LaMnCuO3 perovskite on the reduction of Mn4+ and Cu2+/Cu+ cations. After gold loading, the H2 uptakes of the gold catalysts were even higher than those of the respective perovskite supports, accompanied by a notable shift in the first reduction peak to lower temperatures. This shift is primarily due to H2 activation on the AuNPs and the subsequent spillover of hydrogen atoms to the support [22,44]. Among all the gold catalysts, Au/LaFeCuO3 and Au/LaCoCuO3 showed the most significant increase in H2 uptake (0.3 mmol/g) compared to their perovskite supports. This enhancement can be attributed to the increased oxygen vacancies and adsorbed oxygen species at the gold–support interface, which corresponds to the highest surface (OV + OA)/OL ratio observed in these two catalysts (Figure 3C). These findings suggest that both Cu doping and Au loading in the LaMO3 perovskite supports enhance surface defects, thereby influencing their reducibility. Interestingly, Au/LaMnCuO3 exhibited the highest temperatures for both the starting reduction (~150 °C) and the first reduction peak (~300 °C), indicating a stronger gold–support interaction in this catalyst, where the Cu dopant is less prone to reduction to Cu0.
The temperature-programmed desorption of NH3/CO2 (NH3/CO2-TPD) was utilized to study the acid/base properties of the perovskite supports. The NH3/CO2-TPD profiles are depicted in Figure S3, with the amounts of acidic sites (acidity) and basic sites (basicity) detailed in Table 1. Obviously, both NH3-TPD and CO2-TPD profiles show a maximum desorption peak below 150 °C, indicating that weak acidic and basic sites predominantly occupy the surface of these perovskites. In comparison to LaMO3, the LaMCuO3 perovskites exhibited a significant decrease in both acidity and basicity. Specifically, the amount of acidic sites dropped from 78.9 μmol/g for LaMnO3 to 14.7 μmol/g for LaMnCuO3, while the amount of basic sites decreased from 149.7 μmol/g for LaMnO3 to 41.3 μmol/g for LaNiCuO3. These results indicate that these perovskite supports possess alkaline characteristics, which are advantageous for alcohol dehydrogenation [45,46].

2.2. Catalytic Performance

2.2.1. Support Effect

The catalytic performance of various perovskites and perovskite-supported Au catalysts in the aerobic oxidation of ethanol was investigated. All perovskite supports and catalysts were pretreated at 250 °C with air before being reacted with 2.5 vol% ethanol and 7.5 vol% O2 at a gas hourly space velocity (GHSV) of 100,000 mL gcat−1 h−1. Evidently, the bare LaMO3 and LaMCuO3 perovskites obtained ethanol conversions of 2–9% and 5–25% at 250 °C, respectively, with AC selectivity ranging from 72% to 88% (see Figure S4). In contrast, all Au catalysts showed superior performance compared to the corresponding perovskites. As shown in Table 2, with the exception of Au/LaMnO3, which nearly completely oxidized ethanol, the other Au catalysts obtained 15–93% ethanol conversion and 85–98% AC selectivity at 225 °C. Among the various Au/LaMO3 catalysts, Au/LaNiO3 showed relatively higher AC yield (38%) and space-time yield (STY~155 gAC gAu−1 h−1). Doping Cu into LaMO3 resulted in the Au/LaMCuO3 catalysts, which displayed improved AC yield and STY values compared to their undoped counterparts, despite having half the amount of Au loadings (<0.5 wt%). Notably, Au/LaMnCuO3 achieved the highest AC yield and STY, reaching 91% and 764 h−1, respectively.
Figure 5A,B present the temperature dependence of ethanol conversion, AC selectivity, and yield over various gold catalysts. Among the Au/LaMO3 catalysts, Au/LaFeO3 showed the lowest activity across the temperature range of 100–250 °C, probably due to its limited reducibility, which results in a lack of sufficient redox-active sites, as shown in Figure 4A. Although Au/LaMnO3 exhibited relatively high activity compared to other Au/LaMO3 catalysts, its AC selectivity declined significantly above 200 °C, with CO2 selectivity rising to 93% at 225 °C. This observation aligns with previous studies indicating the complete oxidation capability of the Au/LaMnO3 catalyst at lower temperatures [47]. In contrast, all Au/LaMCuO3 catalysts displayed markedly higher activity and AC selectivity than their corresponding Au/LaMO3 counterparts below 250 °C, highlighting the beneficial effect of Cu doping. Au/LaFeCuO3 achieved a maximum AC yield of 55% at 250 °C, which is double that of Au/LaFeO3. Similarly, Au/LaCoCuO3 and Au/LaNiCuO3 exhibited 3–4 times higher STY values (~500 h−1) at 225 °C, although CO2 selectivity increased dramatically to ~95% at 250 °C. The rise in CO2 selectivity during ethanol oxidation at 250 °C is attributed to the significant reduction of Cu2+/Cu+ and Co3+/Ni3+ species, as indicated by the H2-TPR results (Figure 4B), along with the formation of excess oxygen vacancies and activated oxygen species that facilitate the complete oxidation of ethanol. The enhanced catalytic performance of the three Au/LaMCuO3 (M = Fe, Co, Ni) catalysts can be largely ascribed to the synergistic interactions between AuNPs and surface Cu sites in the Cu-doped perovskite supports [21,22,23]. In contrast, Au/LaMnCuO3, which shares similar gold content, surface area, and acidity/basicity with the other Au/LaMCuO3 catalysts, exhibited the highest AC yield (91%) and STY (764 h−1) at 225 °C. The superior catalytic performance of Au/LaMnCuO3 is likely related to its smaller AuNP size and the lower reducibility of Cu2+/Cu+ and Mn4+/Mn3+ species in the LaMnCuO3 support, which can foster a stable Au0-Cu+ synergy beneficial for the activation of O2 and ethanol [22]. Generally, the catalytic activity follows the order LaMO3 < LaMCuO3 < Au/LaMO3 < Au/LaMCuO3, with Mn as the M demonstrating the highest activity in each series. These findings suggest that both surface-defective Mn3+/Mn2+ and Cu+ sites can facilitate oxygen activation. Thus, a specific Au-Mn-Cu synergy is believed to play a crucial role in the catalytic performance of Au/LaMnCuO3 catalysts.
To further elucidate the support effect, we compared Arrhenius plots obtained at lower temperatures (100–200 °C) and lower conversion levels (<30%). The apparent activation energies (Ea) were calculated to range from 47 to 76 kJ/mol (see Table 2 and Figure 5C), aligning with previously reported values of 30 to 80 kJ/mol for gas-phase ethanol oxidation over supported Au catalysts [16,22]. Generally, Ea values show an inverse correlation with catalytic activity; for instance, the least active Au/LaFeO3 catalyst displays the highest Ea of 76 kJ/mol. Notably, the most active Au/LaMnCuO3 catalyst exhibits the lowest Ea of 47 kJ/mol, highlighting the facile activation of ethanol and O2 reactants on this catalyst.
Given that biomass-derived ethanol can contain up to 90% water and that ethanol purification is energy-intensive [13,48], it is highly desirable to perform selective gas-phase ethanol oxidation using aqueous ethanol feed. To assess the stability of Au/LaMnCuO3, we compared its performance in the presence of anhydrous ethanol (Figure 5D) and 50 wt% aqueous ethanol (Figure 5E). For anhydrous ethanol, the ethanol conversion slightly decreased from 93% to 91% after 60 h on stream at 225 °C, with AC selectivity decreasing marginally from 98% to 97%. To our delight, when using 50 wt% aqueous ethanol, the ethanol conversion slightly dropped from 73% to 66% after 100 h on stream at 200 °C, while the AC yield remained constant at 99%. The average size of the AuNPs in the spent Au/LaMnCuO3 catalyst increased from 3.1 to 3.3 nm after 100 h (Figure S4), indicating that the catalyst can resist sintering under hydrothermal conditions. The Au/LaMnCuO3 catalyst showed even better hydrothermal stability than the previously reported zeolite-encapsulated Au catalysts [48]. These results demonstrate that Au/LaMnCuO3 is an efficient and stable catalyst for the selective gas-phase oxidation of both anhydrous and aqueous ethanol to AC.

2.2.2. Isotope Effect

To gain further insight into the kinetic behavior of ethanol oxidation over the Au/LaMnCuO3 catalyst, we utilized deuterated ethanol molecules: ethanol with a deuterated hydroxyl group (C2H5OD, 99 atom% D, from Sigma-Aldrich, Saint Louis, MO, USA) and fully deuterated ethanol (C2D5OD, 99.5 atom% D, from Sigma-Aldrich). This approach was designed to clarify the kinetic relevance of the cleavage of O-H and α-C-H bonds in ethanol. The kinetic isotope effects (KIEs), defined as the ratio of reaction rates for normal and deuterated ethanol, were measured under the following conditions: 2.5 vol% ethanol, an ethanol/O2 ratio of 1/3, a GHSV of 100,000 mL gcat−1 h−1, and a temperature of 125 °C (Table 3). The observed KIEs for C2H5OD and C2D5OD were 1.5 and 2.8, respectively. These values indicate that the cleavage of both the O-H bond and α-C-H bond of ethanol are rate-controlling steps in the ethanol oxidation process over Au/LaMnCuO3. These findings are consistent with previous studies on gas-phase selective ethanol oxidation over Na-α-MnO2 [6] and Au/Fe-γ-MnO2 [16]. Furthermore, the normal KIE observed for C2H5OD aligns with theoretical calculations for ethanol oxidation catalyzed by Au/MgCuCr2O4, which indicates that the reaction of ethanol with superoxide (O2−) species to dissociate the hydroxyl group has an activation barrier and is endothermic by 24 kJ/mol [17].

2.2.3. Influence of Reaction Conditions

To further elucidate the influence of reaction conditions on the catalytic performance of the optimal Au/LaMnCuO3 catalyst, we evaluated various factors, including oxidant type, O2 and ethanol concentrations, and GHSV, as illustrated in Figure 6A–E. First, we compared the use of O2 as an oxidant for ethanol oxidation with conditions in the absence of O2, as well as in the presence of N2O and a mixture of O2 and H2 (Figure 6A,B). Without O2, the catalyst exhibited very low activity, achieving only 19% conversion at 250 °C, while AC selectivity decreased significantly above 150 °C, with ethylene forming as a byproduct. This decline in selectivity is likely due to increased catalyst acidity resulting from the gradual depletion of surface oxygen species. Similarly, with N2O as the oxidant, Au/LaMnCuO3 showed marked deactivation, which can be ascribed to the slow N2O dissociation over gold catalysts [22,49]. In contrast, co-feeding O2 with H2 led to lower ethanol conversion compared to using O2 alone. This suggests that the activated oxygen species are not hydrogen peroxide (OOH), but rather superoxide (O2−) or peroxide (O22−) [17,22,50], which occupy the oxygen vacancies of surface Mn2+/Cu+ defects and serve as basic sites for ethanol activation.
Figure 6C shows the effect of O2 concentration on catalytic performance at a constant ethanol concentration of 2.5 vol%, a GHSV of 100,000 mL gcat−1 h−1, and a temperature of 125 °C. The Langmuir-type dependence of the reaction rate on O2 concentration suggests that the adsorbed oxygen species become nearly saturated when the O2/ethanol ratio exceeds 3. In contrast, increasing the ethanol concentration from 1 to 10 vol% at an ethanol/O2 ratio of 1/3 revealed a linear dependence of the reaction rate on ethanol concentration (Figure 6D), indicating that the reaction is first-order with respect to ethanol. Figure 6E demonstrates how varying the GHSV (50,000–200,000 mL gcat−1 h−1) affects the performance of Au/LaMnCuO3 while maintaining a constant catalyst amount (0.06 g), ethanol concentration (2.5 vol%), and ethanol/O2 ratio (1/3). Although ethanol conversion decreased with increasing GHSV, the STY value increased linearly, implying that higher AC productivity can be achieved with the Au/LaMnCuO3 catalyst at elevated GHSV. To confirm this, we further evaluated the catalytic performance at a GHSV of 200,000 mL gcat−1 h−1 (Figure 6F). As the temperature increased, ethanol conversion rose linearly from 15% at 150 °C to 83% at 225 °C, with AC selectivity remaining close to 99%. Consequently, the STY of AC increased from 250 to 1378 gAC gcat−1 h−1. The high STY achieved by the Au/LaMnCuO3 catalyst at 225 °C is comparable to that of the previously reported Au/MgCuCr2O4 catalyst at 250 °C [22], highlighting the superior activity of the former catalyst.
Based on the findings, we attribute the enhanced catalytic performance of Cu-doped LaMO3 (M = Mn, Fe, Co, and Ni) perovskite-supported gold catalysts in gas-phase selective ethanol oxidation to improved Au–support synergy. In particular, the optimal Au/LaMnCuO3 catalyst is believed to exhibit a unique Au-Mn-Cu synergy that is more effective than the Au-Cu synergy observed in other Au/LaMCuO3 catalysts. This is due to the greater propensity of the doped Cu2+/Cu+ species in the latter cases to be reduced to Cu0. Moreover, the stabilizing effect of LaMnCuO3 on the Cu+ species facilitates the activation of O2 and ethanol at lower temperatures. Ongoing theoretical calculations aim to further elucidate the nature of the Au-Mn-Cu synergy.

3. Methods

3.1. Catalyst Preparation

All chemicals used in this study were of analytical grade and were purchased from Adamas Reagent Co., Ltd. The LaMO3 and LaMCuO3 (M = Mn, Fe, Co, and Ni) supports were synthesized using a sol–gel combustion method. Nitrates containing La, M, or Cu in stoichiometric amounts (La/M = 1; La/(M + Cu) = 1; M/Cu = 3) for the synthesis of 10 g of product were dissolved in 50 mL of deionized water. Citric acid (6 g) and ethylene glycol (3 mL) were then added to the solution. The resulting mixture was evaporated in a sand bath at 150 °C. The gel was subsequently ignited to obtain an amorphous precursor, which was calcined in air at 900 °C for 5 h to yield the perovskite supports. Various supported Au catalysts were prepared through homogeneous deposition–precipitation of HAuCl4, using urea as the precipitating agent, targeting a gold loading of 1.0 wt.% for Au/LaMO3 and 0.5 wt.% for Au/LaMCuO3. Finally, the catalysts were calcined in air at 300 °C for 5 h.

3.2. Catalyst Characterization

XRD was performed using an Empyrean apparatus with Cu Kα radiation (40 kV and 30 mA). Nitrogen physisorption was conducted on a Tristar 3000 automated gas adsorption system. TEM images were acquired using an FEI Tecnai G2 F30 electron microscope (Hillsboro, OR, USA), and the average size of AuNPs was calculated by measuring ~200 Au particles from several images. The gold loading was determined with a Perkin Elmer (Waltham, MA, USA) AA-300 atomic absorption spectrometer (AAS) after extracting the metal using aqua regia. H2-TPR and NH3/CO2-TPD experiments were performed using a Micrometrics AutoChem 2920II instrument (Norcross, GA, USA). For H2-TPR, the sample was reduced in a mixture of 10 vol% H2 in Ar at a flow rate of 10 mL min−1 while heating from room temperature to 850 °C at a ramp rate of 10 °C min−1. For NH3/CO2-TPD, the sample was pretreated in Ar at 300 °C for 2 h and then cooled to 100 °C and saturated with NH3 or CO2 gas at a flow rate of 30 mL min−1, using 0.3% NH3/Ar or 10% CO2/Ar for 1 h, respectively. Afterward, the sample was flushed with Ar at 100 °C for 1 h to remove physically absorbed NH3 or CO2, followed by heating in Ar from 100 to 500 °C at a rate of 10 °C min−1. XPS measurements were conducted using an AXIS-ULTRA DLD-600W spectrometer (Shimazu-Kratos, Japan) with Al Kα irradiation. The binding energies were calibrated by setting the C 1s peak of adventitious carbon to 284.5 eV.

3.3. Catalytic Activity Measurements

Ethanol oxidation was carried out in a fixed-bed plug flow reactor at atmospheric pressure. The Au catalyst (0.06 g, 80–100 mesh) diluted with α-Al2O3 (0.5 g, 60–80 mesh) was loaded into a quartz reactor with an internal diameter of 8 mm and a thermal couple inside the catalyst bed. Before the reaction, the catalyst was treated with O2 at 250 °C for 2 h. Ethanol (5 μL min−1) was pumped into an evaporator at 83 °C together with O2 (7.5 mL min−1) and N2 (90 mL min−1), which corresponded to a molar ratio of ethanol/O2/N2 = 1/3/36 in the gas phase. The preheated gas mixture was then passed through the catalyst bed at a gas hourly space velocity (GHSV) of ~100,000 mL gcat−1 h−1. The reaction products were analyzed online by GC 9070II (Fuli, Taizhou, China) equipped with a 30 m RB-InnoWax capillary column and a TDX-01 packed column. In all cases, the carbon balance closed at 100 ± 2%.

4. Conclusions

In summary, this study demonstrates the promoting effect of Cu doping on LaMO3 (M = Mn, Fe, Co, and Ni) perovskite-supported gold catalysts for the gas-phase oxidation of ethanol to acetaldehyde. Among the various Au/LaMO3 and Au/LaMCuO3 catalysts, Au/LaMnCuO3, with only 0.45 wt% Au loading, exhibited the highest ethanol conversion (93%), acetaldehyde selectivity (98%), and space-time yield (764 gAC gAu−1 h−1) at 225 °C, outperforming previously reported catalysts. Comprehensive characterization reveals that the superior catalytic performance of Au/LaMnCuO3 can be attributed to the synergistic Au-Mn-Cu interactions between AuNPs and the LaMnCuO3 support, which facilitate the activation of O2 and ethanol at lower temperatures. The normal kinetic isotope effects observed for deuterated ethanol indicate that the dissociation of both the O-H and α-C-H bonds are rate-controlling steps in the oxidation of ethanol over Au/LaMnCuO3. Notably, this optimal catalyst enables the selective oxidation of 50% aqueous ethanol without significant deactivation after 100 h on stream, highlighting its practical applicability. These findings pave the way for the design of more cost-effective and sustainable catalysts for bioethanol valorization.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/catal15020176/s1, Table S1: Lattice parameters of various samples. Figure S1: XRD patterns of various LaMO3 (A) and LaMCuO3 (B) perovskites; Figure S2: M 2p XPS spectra of Au/LaMCuO3 (M = Mn, Fe, Co, Ni) catalysts (A) and O 1s XPS spectra of Au/LaMn(Cu)O3 and Au/LaFe(Cu)O3 catalysts (B); Figure S3: NH3-TPD (A) and CO2-TPD (B) profiles of LaMO3 (A) and LaMCuO3 (B) perovskites; Figure S4: TEM images and gold particle size distribution of spent Au/LaMnCuO3 catalyst.

Author Contributions

Investigation, validation, writing—original draft, and writing—review and editing, L.Y.; investigation and data curation, J.W.; conceptualization, resources, writing—review and editing, supervision, and funding acquisition, P.L. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the National Natural Science Foundation of China (21972050) and the Program for Academic Frontier Youth Team in Huazhong University of Science and Technology (2018QYTD03).

Data Availability Statement

The data supporting the findings of this study are available in the paper and its Supplementary Materials.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Eagan, N.M.; Kumbhalkar, M.D.; Buchanan, J.S.; Dumesic, J.A.; Huber, G.W. Chemistries and Processes for the Conversion of Ethanol into Middle-Distillate Fuels. Nat. Rev. Chem. 2019, 3, 223–249. [Google Scholar] [CrossRef]
  2. Sun, J.; Wang, Y. Recent Advances in Catalytic Conversion of Ethanol to Chemicals. ACS Catal. 2014, 4, 1078–1090. [Google Scholar] [CrossRef]
  3. Dagle, R.A.; Winkelman, A.D.; Ramasamy, K.K.; Lebarbier Dagle, V.; Weber, R.S. Ethanol as a Renewable Building Block for Fuels and Chemicals. Ind. Eng. Chem. Res. 2020, 59, 4843–4853. [Google Scholar] [CrossRef]
  4. He, L.; Zhou, B.C.; Sun, D.H.; Li, W.C.; Lv, W.L.; Wang, J.; Liang, Y.Q.; Lu, A.H. Catalytic Conversion of Ethanol to Oxygen-Containing Value-Added Chemicals. ACS Catal. 2023, 13, 11291–11304. [Google Scholar] [CrossRef]
  5. Pang, J.; Yin, M.; Wu, P.; Li, X.; Li, H.; Zheng, M.; Zhang, T. Advances in Catalytic Dehydrogenation of Ethanol to Acetaldehyde. Green Chem. 2021, 23, 7902–7916. [Google Scholar] [CrossRef]
  6. Liu, P.; Duan, J.; Ye, Q.; Mei, F.; Shu, Z.; Chen, H. Promoting Effect of Unreducible Metal Doping on OMS-2 Catalysts for Gas-Phase Selective Oxidation of Ethanol. J. Catal. 2018, 367, 115–125. [Google Scholar] [CrossRef]
  7. Malmusi, A.; Velasquez Ochoa, J.; Tabanelli, T.; Basile, F.; Lucarelli, C.; Agnoli, S.; Carraro, F.; Granozzi, G.; Cavani, F. Ethanol Aerobic and Anaerobic Oxidation with FeVO4 and V2O5 Catalysts. Appl. Catal. A Gen. 2019, 570, 139–147. [Google Scholar] [CrossRef]
  8. Wang, P.; Duan, J.; Wang, J.; Mei, F.; Liu, P. Elucidating Structure-Performance Correlations in Gas-Phase Selective Ethanol Oxidation and CO Oxidation over Metal-Doped γ-MnO2. Chin. J. Catal. 2020, 41, 1298–1310. [Google Scholar] [CrossRef]
  9. Oefner, N.; Heck, F.; Dürl, M.; Schumacher, L.; Khatoon Siddiqui, H.; Kramm, U.I.; Hess, C.; Möller, A.; Albert, B.; Etzold, B.J.M. Activity, Selectivity and Initial Degradation of Iron Molybdate in the Oxidative Dehydrogenation of Ethanol. ChemCatChem 2022, 14, e202101219. [Google Scholar] [CrossRef]
  10. Wang, J.; Huang, R.; Feng, Z.; Liu, H.; Su, D. Multi-Walled Carbon Nanotubes as a Catalyst for Gas-Phase Oxidation of Ethanol to Acetaldehyde. ChemSusChem 2016, 9, 1820–1826. [Google Scholar] [CrossRef]
  11. Wang, J.; Huang, R.; Zhang, Y.; Diao, J.; Zhang, J.; Liu, H.; Su, D. Nitrogen-Doped Carbon Nanotubes as Bifunctional Catalysts with Enhanced Catalytic Performance for Selective Oxidation of Ethanol. Carbon 2017, 111, 519–528. [Google Scholar] [CrossRef]
  12. Liu, P.; Zhu, X.; Yang, S.; Li, T.; Hensen, E.J.M. On the Metal-Support Synergy for Selective Gas-Phase Ethanol Oxidation over MgCuCr2O4 Supported Metal Nanoparticle Catalysts. J. Catal. 2015, 331, 138–146. [Google Scholar] [CrossRef]
  13. Zhang, J.; Wang, L.; Zhu, L.; Wu, Q.; Chen, C.; Wang, X.; Ji, Y.; Meng, X.; Xiao, F. Solvent-Free Synthesis of Zeolite Crystals Encapsulating Gold-Palladium Nanoparticles for the Selective Oxidation of Bioethanol. ChemSusChem 2015, 8, 2867–2871. [Google Scholar] [CrossRef]
  14. Silbaugh, T.L.; Devlaminck, P.; Sofranko, J.A.; Barteau, M.A. Selective Oxidation of Ethanol over Ag, Cu and Au Nanoparticles Supported on Li2O/γ-Al2O3. J. Catal. 2018, 364, 40–47. [Google Scholar] [CrossRef]
  15. Wang, J.; Luo, H.; Liu, P. Highly Dispersed Gold Nanoparticles on Metal-Doped α-MnO2 Catalysts for Aerobic Selective Oxidation of Ethanol. Catal. Commun. 2020, 142, 106030. [Google Scholar] [CrossRef]
  16. Wang, P.; Luo, H.; Wang, J.; Han, B.; Mei, F.; Liu, P. Synergistic Effect between Gold Nanoparticles and Fe-doped γ-MnO2 toward Enhanced Aerobic Selective Oxidation of Ethanol. Catal. Sci. Technol. 2020, 10, 4332–4339. [Google Scholar] [CrossRef]
  17. Song, W.; Liu, P.; Hensen, E.J.M. A Mechanism of Gas-Phase Alcohol Oxidation at the Interface of Au Nanoparticles and a MgCuCr2O4 Spinel Support. Catal. Sci. Technol. 2014, 4, 2997–3003. [Google Scholar] [CrossRef]
  18. Wang, L.; Wang, L.; Meng, X.; Xiao, F.S. New Strategies for the Preparation of Sinter-Resistant Metal-Nanoparticle-Based Catalysts. Adv. Mater. 2019, 31, 1901905. [Google Scholar] [CrossRef]
  19. Takei, T.; Iguchi, N.; Haruta, M. Synthesis of Acetaldehyde, Acetic Acid, and Others by the Dehydrogenation and Oxidation of Ethanol. Catal. Surv. Asia 2011, 15, 80–88. [Google Scholar] [CrossRef]
  20. Takei, T.; Iguchi, N.; Haruta, M. Support Effect in the Gas Phase Oxidation of Ethanol over Nanoparticulate Gold Catalysts. New J. Chem. 2011, 35, 2227–2233. [Google Scholar] [CrossRef]
  21. Liu, P.; Hensen, E.J.M. Highly Efficient and Robust Au/MgCuCr2O4 Catalyst for Gas-Phase Oxidation of Ethanol to Acetaldehyde. J. Am. Chem. Soc. 2013, 135, 14032–14035. [Google Scholar] [CrossRef]
  22. Liu, P.; Li, T.; Chen, H.; Hensen, E.J.M. Optimization of Au0-Cu+ Synergy in Au/MgCuCr2O4 Catalysts for Aerobic Oxidation of Ethanol to Acetaldehyde. J. Catal. 2017, 347, 45–56. [Google Scholar] [CrossRef]
  23. Du, X.; Fu, N.; Zhang, S.; Chen, C.; Wang, D.; Li, Y. Au/CuSiO3 Nanotubes: High-Performance Robust Catalysts for Selective Oxidation of Ethanol to Acetaldehyde. Nano Res. 2016, 9, 2681–2686. [Google Scholar] [CrossRef]
  24. Royer, S.; Duprez, D.; Can, F.; Courtois, X.; Batiot-Dupeyrat, C.; Laassiri, S.; Alamdari, H. Perovskites as Substitutes of Noble Metals for Heterogeneous Catalysis: Dream or Reality. Chem. Rev. 2014, 114, 10292–10368. [Google Scholar] [CrossRef]
  25. Zhu, J.; Li, H.; Zhong, L.; Xiao, P.; Xu, X.; Yang, X.; Zhao, Z.; Li, J. Perovskite Oxides: Preparation, Characterizations, and Applications in Heterogeneous Catalysis. ACS Catal. 2014, 4, 2917–2940. [Google Scholar] [CrossRef]
  26. Xu, X.; Wang, W.; Zhou, W.; Shao, Z. Recent Advances in Novel Nanostructuring Methods of Perovskite Electrocatalysts for Energy-Related Applications. Small Methods 2018, 2, 1800071. [Google Scholar] [CrossRef]
  27. Chen, S.; Su, Y.; Deng, P.; Qi, R.; Zhu, J.; Chen, J.; Wang, Z.; Zhou, L.; Guo, X.; Xia, B.Y. Highly Selective Carbon Dioxide Electroreduction on StructureEvolved Copper Perovskite Oxide toward Methane Production. ACS Catal. 2020, 10, 4640–4646. [Google Scholar] [CrossRef]
  28. Zhou, C.; Liu, X.; Wu, C.; Wen, Y.; Xue, Y.; Chen, R.; Zhang, Z.; Shan, B.; Yin, H.; Wang, W.G. NO Oxidation Catalysis on Copper Doped Hexagonal Phase LaCoO3: A Combined Experimental and Theoretical Study. Phys. Chem. Chem. Phys. 2014, 16, 5106–5112. [Google Scholar] [CrossRef]
  29. Zhang, X.; Dai, J.; Ding, J.; Tan, K.B.; Zhan, G.; Huang, J.; Li, Q. Activation of Molecular Oxygen over Mn-Doped La2CuO4 Perovskite for Direct Epoxidation of Propylene. Catal. Sci. Technol. 2022, 12, 2426–2437. [Google Scholar] [CrossRef]
  30. Duma, Z.G.; Swartbooi, A.; Musyoka, N.M. Thermocatalytic Decomposition of Methane to Low-Carbon Hydrogen using LaNi1-xCuxO3 Perovskite Catalysts. Appl. Catal. A Gen. 2024, 677, 119703. [Google Scholar] [CrossRef]
  31. Arrii, S.; Morfin, F.; Renouprez, A.J.; Rousset, J.L. Oxidation of CO on Gold Supported Catalysts Prepared by Laser Vaporization: Direct Evidence of Support Contribution. J. Am. Chem. Soc. 2004, 126, 1199–1205. [Google Scholar] [CrossRef] [PubMed]
  32. Liu, P.; Degirmenci, V.; Hensen, E.J.M. Unraveling the Synergy Between Gold Nanoparticles and Chromium-Hydrotalcites in Aerobic Oxidation of Alcohols. J. Catal. 2014, 313, 80–91. [Google Scholar] [CrossRef]
  33. Chen, H.; Xu, Y.; Zhu, K.; Zhang, H. Understanding oxygen-deficient La2CuO4-δ perovskite activated peroxymonosulfate for bisphenol A degradation: The role of localized electron within oxygen vacancy. Appl. Catal. B Environ. 2021, 284, 119732. [Google Scholar] [CrossRef]
  34. Sun, M.; Li, W.; Zhang, B.; Cheng, G.; Lan, B.; Ye, F.; Zheng, Y.; Cheng, X.; Yu, L. Enhanced Catalytic Performance by Oxygen Vacancy and Active Interface Originated from Facile Reduction of OMS-2. Chem. Eng. J. 2018, 331, 626–635. [Google Scholar] [CrossRef]
  35. Yin, X.; Shen, L.; Wang, S.; Wang, B.; Shen, C. Double adjustment of Co and Sr in LaMnO3+δ perovskite oxygen carriers for chemical looping steam methane reforming. Appl. Catal. B Environ. 2022, 301, 120816. [Google Scholar] [CrossRef]
  36. Hu, W.; Li, D.; Yang, Y.; Li, T.; Chen, H.; Liu, P. Copper Ferrite Supported Gold Nanoparticles as Efficient and Recyclable Catalyst for Liquid-Phase Ethanol Oxidation. J. Catal. 2018, 357, 108–117. [Google Scholar] [CrossRef]
  37. Chu, K.; Zong, W.; Xue, G.; Guo, H.; Qin, J.; Zhu, H.; Zhang, N.; Tian, Z.; Dong, H.; Miao, Y.E.; et al. Cation Substitution Strategy for Developing Perovskite Oxide with Rich Oxygen Vacancy-Mediated Charge Redistribution Enables Highly Efficient Nitrate Electroreduction to Ammonia. J. Am. Chem. Soc. 2023, 145, 21387–21396. [Google Scholar] [CrossRef]
  38. Deka, D.J.; Gunduz, S.; Fitzgerald, T.; Miller, J.T.; Co, A.C.; Ozkan, U.S. Production of syngas with controllable H2/CO ratio by high temperature co-electrolysis of CO2 and H2O over Ni and Co-doped lanthanum strontium ferrite perovskite cathodes. Appl. Catal. B Environ. 2019, 248, 487–503. [Google Scholar] [CrossRef]
  39. Hou, Y.C.; Ding, M.W.; Liu, S.K.; Wu, S.K.; Lin, Y.C. Ni-Substituted LaMnO3 Perovskites for Ethanol Oxidation. RSC Adv. 2014, 4, 5329–5338. [Google Scholar] [CrossRef]
  40. Yang, J.; Hu, S.; Fang, Y.; Hoang, S.; Li, L.; Yang, W.; Liang, Z.; Wu, J.; Hu, J.; Xiao, W.; et al. Oxygen Vacancy Promoted O2 Activation over Perovskite Oxide for Low-Temperature CO Oxidation. ACS Catal. 2019, 9, 9751–9763. [Google Scholar] [CrossRef]
  41. Zhang, C.; Wang, C.; Hua, W.; Guo, Y.; Lu, G.; Gil, S.; Giroir-Fendler, A. Relationship between Catalytic Deactivation and Physicochemical Properties of LaMnO3 Perovskite Catalyst during Catalytic Oxidation of Vinyl Chloride. Appl. Catal. B Environ. 2016, 186, 173–183. [Google Scholar] [CrossRef]
  42. Qin, Y.; Shen, F.; Zhu, T.; Hong, W.; Liu, X. Catalytic Oxidation of Ethyl Acetate over LaBO3 (B = Co, Mn, Ni, Fe) Perovskites Supported Silver Catalysts. RSC Adv. 2018, 8, 33425–33431. [Google Scholar] [CrossRef] [PubMed]
  43. Pan, F.; Zhang, W.; Ferronato, C.; Valverde, J.L.; Giroir-Fendler, A. Boosting Propene Oxidation Activity over LaFeO3 Perovskite Catalysts by Cobalt Substitution. Appl. Catal. A Gen. 2022, 643, 118779. [Google Scholar] [CrossRef]
  44. Li, X.; Dai, H.; Deng, J.; Liu, Y.; Xie, S.; Zhao, Z.; Wang, Y.; Guo, G.; Arandiyan, H. Au/3DOM LaCoO3: High-Performance Catalysts for the Oxidation of Carbon Monoxide and Toluene. Chem. Eng. J. 2013, 228, 965–975. [Google Scholar] [CrossRef]
  45. Liu, P.; Guan, Y.; van Santen, R.A.; Li, C.; Hensen, E.J.M. Aerobic Oxidation of Alcohols over Hydrotalcite-Supported Gold Nanoparticles: The Promotional Effect of Transition Metal Cations. Chem. Commun. 2011, 47, 11540–11542. [Google Scholar] [CrossRef] [PubMed]
  46. Liu, P.; Li, C.; Hensen, E.J.M. Efficient Tandem Synthesis of Methyl Esters and Imines by Using Versatile Hydrotalcite-Supported Gold Nanoparticles. Chem. Eur. J. 2012, 18, 12122–12129. [Google Scholar] [CrossRef]
  47. Liu, Y.; Dai, H.; Deng, J.; Zhang, L.; Gao, B.; Wang, Y.; Li, X.; Xie, S.; Guo, G. PMMA-Templating Generation and High Catalytic Performance of Chain-like Ordered Macroporous LaMnO3 Supported Gold Nanocatalysts for the Oxidation of Carbon Monoxide and Toluene. Appl. Catal. B Environ. 2013, 140–141, 317–326. [Google Scholar] [CrossRef]
  48. Mielby, J.; Abildstrøm, J.O.; Wang, F.; Kasama, T.; Weidenthaler, C.; Kegnæs, S. Oxidation of Bioethanol Using Zeolite-Encapsulated Gold Nanoparticles. Angew. Chem. Int. Ed. 2014, 53, 12513–12516. [Google Scholar] [CrossRef] [PubMed]
  49. Sobolev, V.T.; Koltunov, K.Y. Gas-phase Oxidation of Alcohols with O2 and N2O Catalyzed by Au/TiO2: A Comparative Study. Catal. Lett. 2015, 145, 583–588. [Google Scholar] [CrossRef]
  50. Song, W.; Perez Ferrandez, D.M.; van Haandel, L.; Liu, P.; Alexander Nijhuis, T.; Hensen, E.J.M. Selective Propylene Oxidation to Acrolein by Gold Dispersed on MgCuCr2O4 Spinel. ACS Catal. 2015, 5, 1100–1111. [Google Scholar] [CrossRef]
Catalysts 15 00176 g001
Figure 1. XRD spectra of (A) Au/LaMO3 and (B) Au/LaMCuO3.
Figure 1. XRD spectra of (A) Au/LaMO3 and (B) Au/LaMCuO3.
Catalysts 15 00176 g001
Catalysts 15 00176 g002aCatalysts 15 00176 g002b
Figure 2. TEM images and Au particle size distributions for (a) Au/LaMnO3, (b) Au/LaFeO3, (c) Au/LaCoO3, (d) Au/LaNiO3, (e) Au/LaMnCuO3, (f) Au/LaFeCuO3, (g) Au/LaCoCuO3, and (h) Au/LaNiCuO3.
Figure 2. TEM images and Au particle size distributions for (a) Au/LaMnO3, (b) Au/LaFeO3, (c) Au/LaCoO3, (d) Au/LaNiO3, (e) Au/LaMnCuO3, (f) Au/LaFeCuO3, (g) Au/LaCoCuO3, and (h) Au/LaNiCuO3.
Catalysts 15 00176 g002aCatalysts 15 00176 g002b
Catalysts 15 00176 g003
Figure 3. XPS spectra of the Au/LaMCuO3 catalysts. (A) Au 4f, (B) Cu 2p, and (C) O 1s.
Figure 3. XPS spectra of the Au/LaMCuO3 catalysts. (A) Au 4f, (B) Cu 2p, and (C) O 1s.
Catalysts 15 00176 g003
Catalysts 15 00176 g004
Figure 4. H2-TPR profiles of various Au/LaMO3 (A) and Au/LaMCuO3 (B) catalysts (the dashed line represents the profile of the corresponding support).
Figure 4. H2-TPR profiles of various Au/LaMO3 (A) and Au/LaMCuO3 (B) catalysts (the dashed line represents the profile of the corresponding support).
Catalysts 15 00176 g004
Catalysts 15 00176 g005
Figure 5. Catalytic performance of Au/LaMO3 (A) and Au/LaMCuO3 (B) catalysts. Arrhenius curve of Au/LaMCuO3 for ethanol oxidation (C). Catalytic stability of Au/LaMnCuO3 using anhydrous ethanol as the feed at 225 °C (D) and 50 wt.% aqueous ethanol at 200 °C (E). (Reaction conditions: 0.06 g catalyst; 5 μL min−1 ethanol; ethanol/O2/N2 = 1/3/36; GHSV = 100,000 mL gcat−1 h−1.)
Figure 5. Catalytic performance of Au/LaMO3 (A) and Au/LaMCuO3 (B) catalysts. Arrhenius curve of Au/LaMCuO3 for ethanol oxidation (C). Catalytic stability of Au/LaMnCuO3 using anhydrous ethanol as the feed at 225 °C (D) and 50 wt.% aqueous ethanol at 200 °C (E). (Reaction conditions: 0.06 g catalyst; 5 μL min−1 ethanol; ethanol/O2/N2 = 1/3/36; GHSV = 100,000 mL gcat−1 h−1.)
Catalysts 15 00176 g005
Catalysts 15 00176 g006
Figure 6. Effects of oxidant (A,B), concentration of O2 (C) and ethanol (D), GHSV (E), and temperature (F) on the catalytic performance of ethanol oxidation over Au/LaMnCuO3 catalysts. (General reaction conditions: 0.06 g catalyst; 0–20 vol% O2; 1–10 vol% ethanol; GHSV = 50,000–200,000 h−1. (A,B): 2.5 vol% ethanol; ethanol/N2O/N2 = 1/3/36; ethanol/O2/H2/N2 = 1/3/1/35; ethanol/O2/N2 = 1/3/36; ethanol/N2 = 1/39; GHSV = 100,000 h−1. (C): 2.5 vol% ethanol; GHSV = 100,000 h−1. (D): ethanol/O2 = 1/3; GHSV = 100,000 h−1. (E): 2.5 vol% ethanol; ethanol/O2 = 1/3. (F): 2.5 vol% ethanol; ethanol/O2 = 1/3; GHSV = 200,000 h−1).
Figure 6. Effects of oxidant (A,B), concentration of O2 (C) and ethanol (D), GHSV (E), and temperature (F) on the catalytic performance of ethanol oxidation over Au/LaMnCuO3 catalysts. (General reaction conditions: 0.06 g catalyst; 0–20 vol% O2; 1–10 vol% ethanol; GHSV = 50,000–200,000 h−1. (A,B): 2.5 vol% ethanol; ethanol/N2O/N2 = 1/3/36; ethanol/O2/H2/N2 = 1/3/1/35; ethanol/O2/N2 = 1/3/36; ethanol/N2 = 1/39; GHSV = 100,000 h−1. (C): 2.5 vol% ethanol; GHSV = 100,000 h−1. (D): ethanol/O2 = 1/3; GHSV = 100,000 h−1. (E): 2.5 vol% ethanol; ethanol/O2 = 1/3. (F): 2.5 vol% ethanol; ethanol/O2 = 1/3; GHSV = 200,000 h−1).
Catalysts 15 00176 g006
Table 1. Textural and physicochemical properties of various supported gold catalysts.
Table 1. Textural and physicochemical properties of various supported gold catalysts.
CatalystdAu a
(nm)		[Au] b (wt%)SBET (m2/g)H2 Uptake c
(mmol/g)		Acidity d
(μmol/g)		Basicity e
(μmol/g)
Au/LaMnO32.50.955.33.3 (3.3)78.9149.7
Au/LaFeO32.30.984.80.2 (0.1)73.5145.3
Au/LaCoO32.50.973.85.8 (5.8)67116.1
Au/LaNiO32.70.936.55.9 (5.8)72.9123.5
Au/LaMnCuO33.10.452.23.6 (3.5)14.750.1
Au/LaFeCuO35.50.474.21.2 (0.9)65.2107.7
Au/LaCoCuO34.50.4326.3 (6.0)33.581.2
Au/LaNiCuO35.30.484.66.1 (6.0)17.841.3
a Based on the TEM result. b Based on the AAS result. c Evaluated by H2-TPR; the data in parentheses are the H2 uptake of the corresponding perovskite supports. d Evaluated by NH3-TPD. e Evaluated by CO2-TPD.
Table 2. Catalytic activity results for Au/LaMO3 and Au/LaMCuO3 catalysts.
Table 2. Catalytic activity results for Au/LaMO3 and Au/LaMCuO3 catalysts.
CatalystConv. (%) aSelec. (%) aYield (%) aSTY (h−1) bEa (kJ/mol) c
Au/LaMnO397551966
Au/LaFeO31595145576
Au/LaCoO332902911268
Au/LaNiO345853815565
Au/LaMnCuO393989176447
Au/LaFeCuO339973830470
Au/LaCoCuO362976052865
Au/LaNiCuO366966349858
a Ethanol conversion, acetaldehyde selectivity, and yield at 225 °C (0.06 g catalyst; 5 μL min−1 ethanol; ethanol/O2/N2 = 1/3/36; GHSV = 100,000 mL gcat−1 h−1). b Space-time yield in gAC gAu−1 h−1, STY = ethanol flow rate (mmol h−1) × conversion × selectivity × molar mass of AC/(catalyst mass × Au content). c Apparent activation energy evaluated at reaction temperature between 100 and 200 °C.
Table 3. Kinetic isotope effects for ethanol oxidation on Au/LaMnCuO3 at 125 °C.
Table 3. Kinetic isotope effects for ethanol oxidation on Au/LaMnCuO3 at 125 °C.
ReactantConv.Selec.ActivityKIE
(kH/kD)
(%)(%)(mmol gcat−1 h−1)
C2H5OH8.899.57.5--
C2H5OD6.099.05.11.5
C2D5OD3.299.02.72.8
Reaction conditions: 0.06 g catalyst; 5 μL min−1 ethanol; ethanol/O2/N2 = 1/3/36; GHSV = 100,000 mL gcat−1 h−1.
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Yue, L.; Wang, J.; Liu, P. Promoting Effect of Copper Doping on LaMO3 (M = Mn, Fe, Co, Ni) Perovskite-Supported Gold Catalysts for Selective Gas-Phase Ethanol Oxidation. Catalysts 2025, 15, 176. https://doi.org/10.3390/catal15020176

AMA Style

Yue L, Wang J, Liu P. Promoting Effect of Copper Doping on LaMO3 (M = Mn, Fe, Co, Ni) Perovskite-Supported Gold Catalysts for Selective Gas-Phase Ethanol Oxidation. Catalysts. 2025; 15(2):176. https://doi.org/10.3390/catal15020176

Chicago/Turabian Style

Yue, Lijun, Jie Wang, and Peng Liu. 2025. "Promoting Effect of Copper Doping on LaMO3 (M = Mn, Fe, Co, Ni) Perovskite-Supported Gold Catalysts for Selective Gas-Phase Ethanol Oxidation" Catalysts 15, no. 2: 176. https://doi.org/10.3390/catal15020176

APA Style

Yue, L., Wang, J., & Liu, P. (2025). Promoting Effect of Copper Doping on LaMO3 (M = Mn, Fe, Co, Ni) Perovskite-Supported Gold Catalysts for Selective Gas-Phase Ethanol Oxidation. Catalysts, 15(2), 176. https://doi.org/10.3390/catal15020176

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop