Binary spinel cobaltites of nickel,copper and zinc as precursors of catalysts for carbon oxides methanation

The hydrogenation of carbon oxides (CO and CO₂) on bimetallic Cu/Co and Ni/Co as well as Co/ZnO catalysts obtained by reduction of the corresponding spinel cobaltites Me_xCo_3-xO₄ is investigated. The predominant hydrogenation process is methanation and in the case of nickel cobaltite high and stable activity and selectivity are reached, no carbon deposition and carbide formation being observed.     

Selective synthesis of alcohols from syngas and hydroformylation of ethylene over supported cluster-derived cobalt catalysts

Hydroformylation of ethylene and CO hydrogenation were studied over cobalt-based catalysts derived from reaction of Co₂(CO)₈ with ZnO, MgO and La₂O₃ supports. At 433 K a similar activity sequence was reached for both reactions: Co/ ZnO > Co/La₂O₃ > Co/MgO. This confirms the deep analogy between hydroformylation and CO hydrogenation into alcohols. In the CO hydrogenation the selectivity towards alcohol mixture (C₁-C₃) was found to be near 100% at 433 K for a conversion of 6% over the Co/ZnO catalyst; this catalyst showed oxo selectivity higher than 98% in the hydroformylation of ethylene. Magnetic experiments showed that no metallic cobalt particles were formed at 433 K. It is suggested that the active site for the step that is common to both reactions is related to the surface homonuclear Co²⁺/[Co(CO)₄]^– ion-pairing species.     

Low-temperature reforming of ethanol over CeO2-supported Ni-Rh bimetallic catalysts for hydrogen production

A new series of Ni-Rh bimetallic catalysts with different Ni and Rh loadings on a high-surface-area CeO₂ was developed for the reforming of bio-ethanol at low-temperature (below 450 °C) to produce H₂-rich gas for on-site or on-board fuel cell applications. Oxidative steam reforming of ethanol (OSRE) over a Ni-Rh/CeO₂ catalyst containing 5 wt% Ni and 1 wt% Rh was found to be more efficient offering about 100% ethanol conversion at 375 °C with high H₂ and CO₂ selectivity and low CO selectivity compared to the steam reforming of ethanol (SRE) reaction which required a higher temperature of about 450 °C to achieve 100% ethanol conversion. The high temperature SRE reaction favors the formation of large amount of CO, which would make the downsteam CO cleanup more complicated for polymer electrolyte membrane fuel cell (PEMFC). The presence of O₂ in the feed gas was found to greatly enhance the conversion of ethanol to produce H₂ and CO₂ as major products. Increase in Ni content above 5 wt% in the catalyst formulation decreased the H₂ selectivity while the selectivity of undesirable CH₄ and acetaldehyde increased. The 1 wt% Rh/CeO₂ catalyst was twice as active as 10 wt% Ni/CO₂ catalyst in terms of ethanol conversion and acetaldehyde selectivity and this indicated that Rh was more effective in C–C bond cleavage than Ni. The reaction was found to proceed through the formation of acetaldehyde intermediate, which subsequently underwent decomposition to produce a mixture of CO and CH₄ or reforming with H₂O and O₂ to produce CO, CO₂ and H₂. The role of Rh is mainly to cleave the C–C and C–H bonds of ethanol to produce H₂ and COx while Ni addition helps converting CO into CO₂ and H₂ by WGS reaction under the conditions employed.     

The supported CeO2/Co3O4–MnO2/CeO2 catalyst on activated carbon prepared by a successive-loading approach with superior catalytic activity and selectivity for CO preferential oxidation in H2-rich stream

The supported CeO₂/Co₃O₄–MnO₂/CeO₂ catalyst on activated carbon (AC) prepared by a successive loading approach to support ceria, cobalt-manganese oxide and ceria on activated carbon exhibits superior catalytic activity and selectivity to Co₃O₄–MnO₂–CeO₂/AC prepared by a one-step loading for CO preferential oxidation in H₂-rich stream, although the same loading of Co, Mn and Ce was used, which illustrates that the addition of ceria doesn't always enhance catalytic performance in CO PROX reaction, and appreciate supporting method is essential. The superior catalytic activity and selectivity of developed catalyst can be ascribed to high reducibility, well dispersion, unique porous structure, and strong interaction between Co₃O₄–MnO₂ and CeO₂.     

Partial oxidation of ethanol over Pd/CeO2 and Pd/Y2O3 catalysts

The effect of the support nature on the performance of Pd catalysts during partial oxidation of ethanol was studied. H₂, CO₂ and acetaldehyde formation was favored on Pd/CeO₂, whereas CO production was facilitated over Pd/Y₂O₃ catalyst. According to the reaction mechanism, determined by DRIFTS analyses, some reaction pathways are favored depending on the support nature, which can explain the differences observed on products distribution. On Pd/Y₂O₃ catalyst, the production of acetate species was promoted, which explain the higher CO formation, since acetate species can be decomposed to CH₄ and CO at high temperatures. On Pd/CeO₂ catalyst, the acetaldehyde preferentially desorbs and/or decomposes to H₂, CH₄ and CO. The CO formed is further oxidized to CO₂, which seems to be promoted on Pd/CeO₂ catalyst.     

Steam reforming of ethanol on Ni–CeO2–ZrO2 catalysts: Effect of doping with copper, cobalt and calcium

Steam reforming (SR) and oxidative steam reforming (OSR) of ethanol were investigated over undoped and Cu, Co and Ca doped Ni/CeO₂–ZrO₂ catalyst in the temperature range of 400–650 °C. The nickel loading was kept fixed at 30 wt.% and the loading of Cu and Co was varied from 2 to 10 wt% whereas the Ca loading was varied from 5 to 15 wt.%. The catalysts were characterized by various techniques, such as surface area, temperature programmed reduction, X-Ray diffraction and H₂ chemisorption. For Cu and Co doped catalyst, CuO and Co₃O₄ phases were detected at high loading whereas for Ca doped catalyst, no separate phase of CaO was found. The reducibility and the metal support interactions were different for doped catalysts and varied with the amount and nature of dopants. The hydrogen uptake, nickel dispersion and nickel surface area was reduced with the metal loading and for the Co loaded catalysts the dispersion of Ni and nickel surface area was very low. For Cu and Ca doped catalysts, the activity was increased significantly and the main products were H₂, CO, CH₄ and CO₂. However, the Co doped catalysts showed poor activity and a relatively large amount of C₂H₄, C₂H₆, CH₃CHO and CH₃COCH₃ were obtained. For SR, the maximum enhancement in catalytic activity was obtained with in the order of NCu5. For Cu–Ni catalysts, CH₃CHO decomposition and reforming reaction was faster than ethanol dehydrogenation reaction. Addition of Cu and Ca enhanced the water gas shift (WGS) and acetaldehyde reforming reactions, as a result the selectivity to CO₂ and H₂ were increased and the selectivity to CH₃CHO was reduced significantly. The maximum hydrogen selectivity was obtained for Catalyst N (93.4%) at 650 °C whereas nearly the same selectivity to hydrogen (89%) was obtained for NCa10 catalyst at 550 °C. In OSR, the catalytic activity was in the order N > NCu5 > NCa15 > NCo5. In the presence of oxygen, oxidation of ethanol was appreciable together with ethanol dehydrogenation. For SR reaction, the highest hydrogen yield was obtained on the undoped catalyst at 600 °C. However, with calcium doping the hydrogen yields are higher than the undoped catalyst in the temperature range of 400–550 °C.     

Effect of ZnO facet on ethanol steam reforming over Co/ZnO

The effects of ZnO facets on ethanol steam reforming (ESR) were investigated over Co/ZnO catalysts synthesized using ZnO with different fractions of (10–10) non-polar facet. Co supported on ZnO with a higher fraction of (10–10) non-polar facet shows higher C–C cleavage activity and higher selectivity to CO₂ (lower selectivity to CO) compared with Co supported on ZnO with less (10–10) non-polar facet exposed. The improved ethanol steam reforming performances are attributed to the high fraction of metallic Co stabilized by the ZnO (10–10) non-polar facet, which enhanced C–C cleavage and water-gas-shift (WGS) activities.     

Selective reduction of NOx with hydrocarbons over Co/MFI prepared by sublimation of CoBr2 and other methods

Co/MFI catalysts were prepared by various methods, including wet-ion exchange (WIE), either as such or in combination with impregnation (IMP), solid-state ion exchange (SSI), and sublimation (SUB) of CoCl₂ (at 700°C) or CoBr₂ (at 600°C) onto H/MFI. The catalysts were tested for the reduction of NO_x with CH₄ or iso-C₄H₁₀ in excess O₂. Below 425°C the SUB catalysts show the highest NO_x reduction activity with CH₄ or iso-C₄H₁₀. Above 425°C, the best performance is given by WIE. Below the temperature of maximum N₂ yield, a mixture of Fe/FER and WIE is superior to either catalyst. Addition of 10% H₂O to the feed drastically decreases the N₂ yield in NO_x reduction with CH₄, but increases the activity with iso-C₄H₁₀ under some conditions. Permanent damage of the zeolite lattice as a potential cause for the adverse effect of H₂O in the tests with CH₄ is eliminated, as the original activity is fully restored after calcination. A 100 h test with a wet iso-C₄H₁₀ feed shows excellent stability with a SUB catalyst prepared from CoBr₂.Characterization by XRD, H₂-TPR, and FTIR reveals that WIE contains isolated Co²⁺ and (Co–OH)⁺ ions that are only reducible at 700°C. SUB catalysts show additional TPR peaks at low temperature, including a feature at 220–250°C, ascribed to multinuclear Co oxo-ions. The formation of an NO_y chemisorption complex is most rapid on these catalysts. No oxidation states between Co⁰ and Co²⁺ are detectable; the one-step reduction of Co²⁺ to Co⁰ clusters could be a cause for the unique propensity of Co/MFI to reduce NO_x with CH₄.     

Honeycomb supported Co3O4/CeO2 catalyst for CO/CH4 emissions abatement: Effect of low Pd–Pt content on the catalytic activity

A structured Co₃O₄–CeO₂ composite oxide, containing 30% by weight of Co₃O_4, has been prepared over a cordieritic honeycomb support. The bimetallic, Pd–Pt catalyst has been obtained by impregnation of the supported Co₃O₄–CeO₂ with Pd and Pt precursors in order to obtain a total metal loading of 50 g/ft³.CO, CH₄ combined oxidation tests were performed over the catalyzed monoliths in realistic conditions, namely GHSV = 100,000 h⁻¹ and reaction feed close to emission from bi-fuel vehicles. The Pd–Pt un-promoted Co₃O₄–CeO₂ is promising for cold-start application, showing massive CO conversion below 100 °C, in lean condition.A strong enhancement of the CH₄ oxidation activity, between 400 and 600 °C, has been observed by addition to the Co₃O₄–CeO₂ of a low amount of Pd–Pt metals.     

Temperature-induced evolution of reaction sites and mechanisms during preferential oxidation of CO

Active sites responsible for the preferential oxidation of carbon monoxide were investigated using 4 wt.% Cu–CeO₂ catalysts prepared by flame spray pyrolysis. Surface redox properties of the catalyst were assessed using a series of temperature-programmed reduction (CO, H₂ and mixed) experiments, as well as operando infrared spectroscopy. It was demonstrated that CO and H₂ react at identical surface sites, with CO₂ formation proceeding simultaneously via three distinct Cuⁿ⁺–CO carbonyl species. The origin of high catalytic selectivity towards CO at below 150 °C stems from the carbonyl stabilization effect on the catalyst surface, preventing adsorption and subsequent oxidation of H₂. Under non-selective conditions at higher temperatures, a gradual red-shift and loss of intensity in the carbonyl peak was observed, indicating reduction of Cu⁺ to Cu⁰, and the onset of an alternate redox-type oxidation mechanism where CO and H₂ compete for the oxidation sites. These results for Cu–CeO₂ suggest that improved low-temperature catalytic activity will only be achieved at the expense of reduced high-temperature selectivity and vice versa.     

Dry reforming of methane over LaNi1−yByO3±δ (B = Mg,Co) perovskites used as catalyst precursor

Perovskites LaNiO₃, LaNi_1−xMg_xO_3−δ and LaNi_1−xCo_xO_3−δ were synthesized by auto combustion method. TPR analysis reveled that Mg or Co substituted perovskites were more difficult to reduce. The perovskites were evaluated as catalyst precursors in the dry reforming of methane. Catalysts obtained by reduction of LaNiO₃ and LaNi_1−xMg_xO_3−δ perovskite had the highest catalytic activity for CO₂ reforming of CH₄ at 700 °C using drastic reaction conditions (10 mg of catalyst, a mixture of CH₄/CO₂ without dilution gas). Methane and carbon dioxide conversions were 57% and 67%, respectively, with a H₂/CO ratio equal to 0.47.The presence of cobalt leads to a decrease of the catalytic activity. This decreasing of activity may be attributed to the Co–Ni alloy formation. Computational calculations revealed that Ni atom cleaves the C–H atom while Co is not able to activate the CH₄ molecule. The interaction energy of CH₄ with the Ni and CO atom was 18 kcal/mol and 0.7 kcal/mol, respectively.The catalysts were characterized by TPR, TEM and in situ XRD.     

Cobalt and Copper Composite Oxides as Efficient Catalysts for Preferential Oxidation of CO in H2-Rich Stream

A series of Co–Cu composite oxides with different Co/Cu atomic ratios were prepared by a co-precipitation method. XRD, N₂ sorption, TEM, XPS, H₂-TPR, CO-TPR, CO-TPD and O₂-TPD were used to characterize the structure and redox properties of the composite oxides. Only spinel structure of Co₃O₄ phase was confirmed for the Co–Cu composite oxides with Co/Cu ratios of 4/1 and 2/1, but the particle sizes of these composite oxides decreased evidently compared with Co₃O₄. These composite oxides could be reduced at lower temperatures than Co₃O₄ by either H₂ or CO. CO and O₂ adsorption amounts over the composite oxides were significantly higher than those over Co₃O₄. These results indicated a strong interaction between cobalt and copper species in the composite samples, possibly suggesting the formation of Cu _x Co_3?x O₄ solid solution. For the preferential oxidation of CO in a H₂-rich stream, the Co–Cu composite oxides (Co/Cu = 4/1–1/1) showed distinctly higher catalytic activities than both Co₃O₄ and CuO, and the formation of Cu _x Co_3?x O₄ solid solution was proposed to contribute to the high catalytic activity of the composite catalysts. The Co–Cu composite oxide was found to exhibit higher catalytic activity than several other Co₃O₄-based binary oxides including Co–Ce, Co–Ni, Co–Fe and Co–Zn oxides.     

SELECTIVE CARBON MONOXIDE OXIDATION IN H2-RICH GAS STREAM OVER Co3O4/CeO2/ZrO2, Ag/CeO2/ZrO2, AND MnO2/CeO2/ZrO2 CATALYSTS

Activity and selectivity of selective CO oxidation in an H₂-rich gas stream over Co₃O₄/CeO₂/ZrO₂, Ag/CeO₂/ZrO₂, and MnO₂/CeO₂/ZrO₂ catalysts were studied. Effects of the metaloxide types and metaloxide molar ratios were investigated. XRD, SEM, and N₂ physisorption techniques were used to characterize the catalysts. All catalysts showed mesoporous structure. The best activity was obtained from 80/10/10 Co₃O₄/CeO₂/ZrO₂ catalyst, which resulted in 90% CO conversion at 200°C and selectivity greater than 80% at 125°C. Activity of the Co₃O₄/CeO₂/ZrO₂ catalyst increased with increase in Co₃O₄ molar ratio.     

Water-gas shift reaction over supported Pt and Pt-CeOx catalysts

A comparison study was performed of the water-gas shift (WGS) reaction over Pt and ceria-promoted Pt catalysts supported on CeO₂, ZrO₂, and TiO₂ under rather severe reaction conditions: 6.7 mol% CO, 6.7 mol% CO₂, and 33.2 mol% H₂O in H₂. Several techniques—CO chemisorption, temperature-programmed reduction (TPR), and inductively coupled plasma-atomic emission spectroscopy (ICP-AES)—were employed to characterize the catalysts. The WGS reaction rate increased with increasing amount of chemisorbed CO over Pt/ZrO₂, Pt/TiO₂, and Pt-CeO _x /ZrO₂, whereas no such correlation was found over Pt/CeO₂, Pt-CeO _x /CeO₂, and Pt-CeO _x /TiO₂. For these catalysts in the absence of any impurities such as Na⁺, the WGS activity increased with increasing surface area of the support, showed a maximum value, and then decreased as the surface area of the support was further increased. An adverse effect of Na⁺ on the amount of chemisorbed CO and the WGS activity was observed over Pt/CeO₂. Pt-CeO _x /TiO₂ (51) showed the highest WGS activity among the tested supported Pt and Pt-CeO_x catalysts. The close contact between Pt and the support or between Pt and CeO _x , as monitored by H₂-TPR, is closely related to the WGS activity. The catalytic stability at 583K improved with increasing surface area of the support over the CeO₂- and ZrO₂-supported Pt and Pt-CeO _x catalysts.     

Nature of Surface Deposits on Sulfated Zirconia Used as Catalyst in the Benzoylation of Anisole

The effects of CO₂, CO and H₂ co-reactants on CH₄ pyrolysis reactions catalyzed by Mo/H-ZSM-5 were investigated as a function of reaction temperatures and co-reactant and CH₄ concentrations. Total CH₄ conversion rates were not affected by CO₂ co-reactants, except at high CO₂ pressures, which led to the oxidation of the active MoC _x species, but CH _x intermediates formed in rate-determining C–H bond activation steps increasingly formed CO instead of hydrocarbons as CO₂ concentrations increased. CO formation rates increased with increasing CO₂ partial pressure; all entering CO₂ molecules reacted with CH₄ within the catalyst bed to form two CO molecules at 950-1033 K. In contrast, hydrocarbon formation rates decreased linearly with increasing CO₂ partial pressure and reached undetectable levels at CO₂/CH₄ ratios above 0.075 at 950 K. CO formation continued for a short period of time at these CO₂/CH₄ molar ratios, but then all catalytic activity ceased, apparently as a result of the conversion of active carbide structures to MoO _x . The removal of CO₂ from the CH₄ stream led to gradual catalyst reactivation via reduction-carburization processes similar to those observed during the initial activation of MoO _x /H-ZSM-5 precursors in CH₄. The CO₂/CH₄ molar ratios required to inhibit hydrocarbon synthesis were independent of CH₄ pressure because of the first-order kinetic dependencies of both CH₄ and CO₂ activation steps. These ratios increased from 0.075 to 0.143 as reaction temperatures increased from 950 to 1033 K. This temperature dependence reflects higher activation energies for reductant (CH₄) than for oxidant (CO₂) activation, leading to catalyst oxidation at higher relative oxidant concentrations as temperature increases. The scavenging of CH _x intermediates by CO₂-derived species leads also to lower chain growth probabilities and to a significant inhibition of catalyst deactivation via oligomerization pathways responsible for the formation of highly unsaturated unreactive deposits. CO co-reactants did not influence the rate or selectivity of CH₄ pyrolysis reactions on Mo/H-ZSM-5; therefore, CO formed during reactions of CO₂/CH₄ mixtures are not responsible for the observed effects of CO₂ on reaction rates and selectivities, or in catalyst deactivation rates during CH₄ reactions. H₂ addition studies showed that H₂ formed during CH₄/CO₂ reactions near the bed inlet led to inhibited catalyst deactivation in downstream catalyst regions, even after CO₂ co-reactants were depleted.     

Comparative Study on Partial Oxidation of Methane over Ni/ZrO2, Ni/CeO2 and Ni/Ce–ZrO2 Catalysts

The partial oxidation of methane has been studied by sequential pulse experiments with CH₄ O₂ CH₄ and simultaneous pulse reaction of CH₄/O₂ (2/1) over Ni/CeO₂, Ni/ZrO₂ and Ni/Ce–ZrO₂ catalysts. Over Ni/CeO₂, CH₄ dissociates on Ni and the resultant carbon species quickly migrate to the interface of Ni–CeO₂, and then react with lattice oxygen of CeO₂ to form CO. A synergistic effect between Ni and CeO₂ support contributes to CH₄ conversion. Over Ni/ZrO₂, CH₄ and O₂ are activated on the surface of metallic Ni, and then adsorbed carbon reacts with adsorbed oxygen to produce CO, which is composed of the main path for the partial oxidation of methane. The addition of ceria to zirconia enhances CH₄ dissociation and improves the carbon storage capacity. Moreover, it increases the storage capacity and mobility of oxygen in the catalyst, thus promoting carbon elimination.     

Methane oxidation to acetic acid catalyzed by Pd2+ cations in the presence of oxygen

Synthesis of acetic acid from methane catalyzed by Pd²⁺ cations dissolved in sulfuric acid was investigated to determine the effects of reaction conditions and the mechanism. Acetic acid yield was found to be a strong function of CH₄ and O₂ partial pressures. High O₂/CH₄ ratio and high total pressure delivered the highest yield of acetic acid (14.2 turnovers of Pd²⁺) and the highest retention of Pd²⁺ in solution (96%). Byproducts were sulfur containing compounds (most notably methyl bisulfate) and CO_x, but the acetic acid selectivity was maximized (82%) by lowering the reaction temperature. Methane is activated by Pd(OSO₃H)₂, forming (CH₃)Pd(OSO₃H). CO, generated from the oxidation of methyl bisulfate, inserts into the CH₃Pd bond creating a (CH₃CO)Pd(OSO₃H) species. Reaction of this complex with H₂SO₄ produces acetic acid. Pd²⁺ is reduced to Pd⁰ during the oxidation of methyl bisulfate or CO, and Pd⁰ is reoxidized to Pd²⁺ by H₂SO₄ and O₂.     

Hydrogen Production from Ethanol over Rh–Pd/CeO2 Catalysts

The work presents a study by temperature programmed desorption, in situ infra red spectroscopy and catalytic steam reforming of ethanol (SRE) over CeO₂ and the bimetallic Pd-Rh/CeO₂; comparison with the monometallic catalysts (Rh/CeO₂ and Pd/CeO₂) was also made for the steam reforming study. Comparing TPD of ethanol over CeO₂ and the bimetallic catalysts indicated two main differences: the direct oxidation route to acetate over CeO₂ is suppressed by the presence of the metal and the lowering of the dehydrogenation reaction temperature by about 100 K. In situ IR study indicated that the bimetallic catalyst breaks the carbon–carbon bond of ethanol at low temperature <400 K, as evidenced by the presence of adsorbed CO species. SRE over ½ wt.% Rh–½ wt.% Pd/CeO₂, at 770 K at realistic conditions showed that maximum conversion and selectivity could be achieved. This high activity considering the very small amounts of transition metals on CeO₂ is discussed in light of their electronic and geometric effects.     

Y-Faujasite Encapsulated Co Clusters: Synthesis, Characterization and Theoretical Model as Probe of the Methane Homologation

The adsorption of Co₂(CO)₈ onto the dehydrated Y-faujasite powder under an N₂ atmosphere and onto the tetrahydrofuran slurry of Y-faujasite under a mixed CO and H₂ atmosphere predominately yielded supported Co₄(CO)₁₂ and supported Co₆(CO)₁₆, respectively. The molecular cobalt-carbonyl clusters and their decarbonylated products have been structurally characterized by extended X-ray absorption fine structure (EXAFS). The decarbonylated sample a possesses a cluster of two Co atoms and the decarbonylated sample b has a cluster phase of three Co atoms. The decarbonylated sample a exhibited higher CH₄ conversion and C₂₊ selectivity (C₂₊ selectivity = ∑nC _n(n = 2–5)/∑nC _n (n = 1–5) * 100%) in comparison with the decarbonylated sample b in methane homologation. A density functional theory (DFT) model was employed to calculate Co clusters adsorbed on a silica substrate which simulates Y-faujasite encapsulated Co clusters. The structural geometries, net spin electronic charge densities, energies of the metal–silica and metal–metal interactions in stable geometries are discussed and used to interpret the cluster size dependence of the catalytic activity and selectivity to C ₂₊ hydrocarbons in the methane homologation.     

EXAFS and XPS Investigations of Cu/ZnO Catalysts and Their Interaction with CO and Methanol

Several investigations have been carried out on Cu/ZnO catalysts by employing extended Xray absorption fine structure (EXAFS) and Xray photoelectron spectroscopy (XPS). EXAFS investigations of Cu/ZnO catalysts subjected to hydrogen reduction show the presence of Cu¹⁺ species and Cu microclusters. The proportion of Cu¹⁺ depends on the rate of increase of the reduction temperature and on the amount of alumina added. An XPS study of the interaction of CO with model Cu/ZnO catalysts prepared in situ in the electron spectrometer shows the formation of CO₂ ^-, CO₃ ^2- and C₂O₄ ^2- species, their proportion relative to CO increasing with the Cu¹⁺/Cu⁰ ratio. A study of the interaction of CH₃OH with Cu clusters deposited on ZnO films reveals reversible molecular adsorption and the formation of CH₃O on clean Cu clusters. If the Cu clusters are pretreated with oxygen, however, both CH₃O and HCOO^- species are produced. Model Cu/ZnO catalyst surfaces containing both Cu¹⁺ and Cu⁰ species show interesting oxidation properties. On a Cu⁰-rich catalyst surface, only the CH₃O species is formed on interaction with CH₃OH. On a Cu¹⁺rich surface, the HCOO^- ion is the predominant species.