CO Oxidation Reaction Research Articles

Relationship between Al-loading and CO oxidation activity of mesostructured silica-supported Pt-based catalysts

The supported Pt-based catalysts for CO oxidation have been extensively investigated, but to our best knowledge, no reports about the effect of the Al-incorporation on mesostructured Pt/MCM-41 catalysts can be found. The parent and Al-modified MCM-41 supports, with typical honeycomb structure, were synthesized using the liquid-crystal template mechanism, while supported Pt-catalysts were prepared by the deposition-precipitation method. The fresh samples were characterized by small- and wide-angle X-ray diffraction (SA-XRD and WA-XRD), N2 physisorption and high-resolution transmission electron microscopy (HRTEM, only supports), while reduced catalysts were also characterized by WA-XRD, HRTEM and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of the adsorbed CO molecules at temperatures between 50 and 200 °C. The relationship between Al-loading with the catalytic performance were well-investigated. The MCM-41- and Al-MCM-41-supported Pt-based catalysts showed a good activity, circularity and stability in the CO oxidation reaction. The studied catalytic parameters (XCO, Ea and T50) were improved with the Al-incorporation and correlated with the average particles sizes. The defects formation and even the acidic features, corroborated by the formation of the Pt-carbonyl-hydride species, were also observed in the Al-modified catalysts.

Transformation of alumina-supported Pt-Au alloyed nanoparticles into core-shell Pt@Au structures during high-temperature treatment

A series of alumina-supported bimetallic AuPt catalysts was prepared by decomposition of a double complex salt containing simultaneously gold and platinum. The decomposition was performed in both the reductive and oxidative atmospheres. Monometallic Au/γ-Al2O3 and Pt/γ-Al2O3 catalysts were used as reference samples. Physicochemical characterization of the catalysts has revealed that despite the preparation route and total metal loading, the alloyed nanoparticles are being formed with close values of the average particle size and similar particle size distribution, while the composition and the structure of the particles differ significantly. Thermal aging of the catalysts at 600 and 800 °C leads to redistribution of metals in the alloyed particles and formation of core-shell Pt@Au nanostructures, which results in significant deactivation of the catalysts concerning a model reaction of CO oxidation. The formation of core-shell particles in the case of high-loaded samples was found to prevent the agglomeration process at elevated temperatures.

High-Temperature Co-Electrolysis

High-temperature Solid Oxide Electrolysis Cells (SOECs) possess the unique property to convert carbon dioxide and/or steam with a faradaic efficiency of 1 into carbon monoxide and/or hydrogen, respectively. High-temperature co-electrolysis of steam and carbon dioxide offers a suitable technology to provide 'white' syngas. Syngas, a mixture of hydrogen and carbon monoxide, as well as pure carbon monoxide are used in chemical industry for the synthesis of many basic chemicals as well as synfuels. Using renewable energy sources and the climate gas CO2 the high-temperature CO2 and co-electrolysis technology presents a sustainable alternative to conventional processes. The technology of co-electrolysis allows the adjustment of the H2 to CO ratio required for various down-stream catalytic processes in one step.Investigations of the high-temperature electrolysis of steam or CO2 and the co-electrolysis of a mixture of both in the feed gas were performed on so-called fuel electrode supported cells consisting of a 8mol% yttria stabilized zirconia (8YSZ) electrolyte, a Ni/8YSZ support and fuel electrode and a (La,Sr)(Co,Fe)O3 air electrode. The experiments showed that the performance of the cell during CO2 electrolysis is lower than for steam and co-electrolysis, as is shown in the Figure. The performance can be characterized by the slope of the current-voltage curve, i.e. the area specific resistance (ASR). For the CO2 electrolysis the ASR at 900 °C and 1.5 A·cm-2 amounts to 410 mΩ·cm-2. For steam and co-electrolysis, the ASR values are nearly the same: 245 mΩ·cm-2. The lower performance for CO2 electrolysis is attributed to the slower kinetics of the CO2 reduction reaction compared to the H2O reduction reaction. Similar observations were made in fuel cell operation, in which the CO oxidation reaction is around a factor 5 slower than the H2 oxidation reaction. The similar ASR values for steam and co-electrolysis are attributed to the occurrence of the reverse water gas shift (RWGS) reaction, in which CO2 and H2 react to CO and H2O during co-electrolysis. The slower kinetics of the CO2 reduction reaction are by-passed in the RWGS reaction using the hydrogen generated through the steam reduction.Further experiments were conducted to investigate the role and importance of the RWGS reaction during co-electrolysis. At the boundary to pure CO2 electrolysis, the performance of feed gas mixtures with low steam contents were investigated. First results show a significant increase of the area specific resistance at a reduced (RWGS) equilibrium steam concentration of about 5 %. Above 15 % steam in the feed gas (in the RWGS equilibrium) the ASR is no longer influenced by the feed gas composition and similar to that of pure steam electrolysis. Experimental results are furthermore compared to theoretical calculations of syngas production on a thermodynamic and partially kinetic level. Figure 1

Highly Active and Stable Fe/SiO2 Catalyst Synthesized by Atomic Layer Deposition for CO Oxidation

Highly dispersed Fe nanoparticles (NPs) were deposited on SiO2 NPs by atomic layer deposition (ALD) in a scalable fluidized bed reactor at 400 oC. In CO oxidation reactions, over the Fe/SiO2 catalyst, Fe2O3 played a vital role. In a long-term stability test of more than 300 h of CO oxidation reaction, there was almost no activity decrease of Fe/SiO2 at 550 oC.

Effect of advanced intake valve closing on the thermo-chemical characteristics of the homogeneous combustion in a DME fueled HCCI engine

This numerical study was performed to analyze the thermo-chemical characteristics of homogeneous combustion on the effect of advanced intake valve closing timing in a DME fueled HCCI engine. To achieve this, the engine simulation was performed using the detailed chemical kinetic mechanism, including 453 reactions for dimethyl ether (CH3OCH3), and the modified NOX mechanism was applied to analyze the NOX reaction pathway of the DME combustion. The experimental study was performed to validate the engine analysis using a single cylinder CI engine with the injection timing of BTDC 40 degree and IVC timing of BTDC 128 degree. The injection quantity and pressure were set to 8 mg and 50 MPa at 1500 RPM, respectively. The results of engine performance such as cylinder pressure, cylinder temperature, heat release rate, and IMEP were decreased and the ISFC and ignition delay were increased when the IVC timing was advanced since the overall rates of a chemical reaction and the reaction rate of OH radicals are reduced. Especially, the reduction of CH2OCH2O2H radicals was a very important factor it affects the ignition delay in the low temperature reaction. Consequently, it influences the LTC and HTC reactions and makes a difference in the fuel oxidation rate and combustion reaction. Furthermore, the OH radicals also had the greatest effect to the CO oxidation and NOX production. The CO and NOX emissions were primarily occurred by the forward reactions of HCO + O2 → CO + HO2 and HO2 + NO → NO2 + OH during the combustion period, respectively. The chemical reactivity and CO oxidation reaction were reduced as the fuel mass fraction increased in the low combustion temperature. In addition, the reaction path of NOX emission related to the thermal NOX reaction did not occur due to the low combustion temperature. Thus, the thermo-chemical characteristics of the DME homogeneous combustion of this work suggest that the chemical reaction of fuel oxidation and exhaust emissions are limited as the effect of chemical oxidation rate, reaction rate, and the OH radical depending on the IVC timing changes.

(Ni,Cu)/hexagonal BN nanohybrids – New efficient catalysts for methanol steam reforming and carbon monoxide oxidation

This work is aimed at the development of bimetallic (Ni0.2Cu0.8) catalysts with hexagonal boron nitride (h-BN) nanosheet (BNNS) supports and elucidating their catalytic activity in the methanol steam reforming and CO oxidation reactions. The hybrid Ni0.2Cu0.8/BN catalysts consist of curved h-BN nanosheets, up to 10–20 nm in lateral size, decorated with metallic nanoparticles, 3.0–8.2 nm in dimensions. The methanol conversion starts at ~20 °C and is nearly completed at 320 °C. The (Ni0.2Cu0.8)/BN nanohybrids exhibit high catalytic stability and high selectivity for CO2 over the whole temperature range. No carbon monoxide is detected during full methanol conversion. The possible mechanism of CO utilization during methanol reforming is proposed using ab initio calculations. The onset temperature of catalytic CO oxidation is 100 °C and full conversion is completed at 200 °C. These results indicate high catalytic efficiency of (Ni0.2Cu0.8)/BN nanohybrids in methanol steam reforming and CO oxidation reactions.

Cu, Sm co-doping effect on the CO oxidation activity of CeO2. A combined experimental and density functional study

The co-doping effect of a rare earth (RE) metal and a transition metal (TM) on ceria oxidation catalysis through the evaluation of samarium-copper co-doped catalysts with Ce-Sm-xCu-O (x: 0–20 at.%, Ce/Sm = 1) nominal compositions, is discussed. The CO oxidation reaction was used as a prototype reaction due to its pivotal role in the fuel cell technology. Ce-Sm-20Cu-O catalyst presented a 64% increase in the CO oxidation activity compared to that of pristine ceria. Diffraction and Raman studies proved that the Cu, Sm co-doping induces many defects related to the dopants (Sm, Cu) and the oxygen vacant sites, while the presence of hybrid CuO/Ce-Sm(Cu)-O fluorite/SmO8 (cubic metastable) phases is the most representative scenario of this oxide microstructure. A size polydispersity of CuO phases was achieved by introducing air cooling during the microwave heating. Cu, Sm atoms were uniformly doped in CeO2 structure according to the HAADF-STEM studies. These results are in agreement with EDS analysis, where Cu, Sm and Ce are located in all the analyzed areas without any preferential distribution. The XPS studies demonstrated the co-presence of Cu2+/Cu1+ and Ce4+/Ce3+ redox couples in agreement with the Bader charge analysis from the ab initio calculations, the latter influencing greatly the oxidation activity of the catalysts. Density functional theory (DFT) calculations shed light on the oxide surface and the underlying mechanism governing the oxidation catalysis taking place. In particular, Cu2+ and Sm3+ dopants were found to be located in the nearest neighbor (NN) sites of oxygen vacancies. Different oxygen vacancies configurations were studied (single vs. double, surface vs. subsurface), where the single vacancies are more stable on the surface, whereas the double vacancies configurations are more stable on the subsurface. Regarding the Ce3+ location, in the presence of single and double oxygen vacancy, the Ce3+ ions prefer to be located in the 1st NN/2nd NN and 2nd NN of the first Ce layer, relative to the oxygen vacancy, respectively. The total Density of States (DOS) analysis of the co-doped systems revealed that the dopants induced new surface states inside the ceria band gap, which can accommodate the unpaired electrons of the vacant oxygen sites. These electronic modifications justify the much lower energy of oxygen vacancy formation (Evf) in both cases, the Sm-doped, and Cu, Sm -doped CeO2 (1 1 1) geometries. Specifically, the Evf lowering upon doping was found to be almost two times larger for the Cu adjacent oxygen vacancies (Cu2+-□) compared to the Sm ones (Sm3+-□), consistent with the CO adsorption trend as the Cu-Sm-CeO2 (1 1 1) system is energetically more favorable than the Sm-CeO2 (1 1 1) and pure CeO2 (1 1 1) surfaces.

Porous Pd‐PdO Nanotubes for Methanol Electrooxidation

AbstractPalladium (Pd) nanostructures are highly active non‐platinum anodic electrocatalysts in alkaline direct methanol fuel cells (ADMFCs) and their electrocatalytic performance relies highly on their morphology and composition. Herein, a facile high‐temperature pyrolysis method to synthesize high‐quality Pd‐palladium oxide (PdO) porous nanotubes (PNTs) by using Pd(II)‐dimethylglyoxime complex (Pd(II)‐DMG) nanorods as a self‐template is reported. The chemical component of pyrolysis products highly correlates with pyrolysis temperature. The electrochemical measurements and density functional theory calculations show the existence of PdO enhances the electroactivity of metallic Pd for both methanol oxidation reaction (MOR) and carbon monoxide oxidation reaction in alkaline media. Benefiting from its one‐dimensionally porous architecture and evident synergistic effect between PdO and Pd (e.g., electronic effect and bifunctional mechanism), Pd‐PdO PNTs achieve a 3.7‐fold mass activity enhancement and improved durability for MOR compared to commercial Pd nanocrystals. Considering the simple synthesis, excellent activity, and long‐term stability, Pd‐PdO PNTs may be highly promising anodic electrocatalysts in ADMFCs.

Exsolution of nickel alloys anchored nanoparticles on perovskite oxides for CO oxidation

Noble metals notably platinum (Pt), is a major element of heterogeneous catalysts, excel in catalysing an extensive number of important catalytic reactions in chemical and automotive industries. Since the increased use of these metals is severely limited because of their high cost and scarcity’s, there is therefore an urgent need for the search of alternative transition metal catalysts that are cheaper and more widely available. This can only be practical if the main drawbacks of these transition metals can be impeded for instance the agglomeration of particles under high temperatures operational conditions with their activity enhanced, such that they can directly replace Pt on a weight-to-weight basis. The exsolution of metallic nanoparticles mainly nickel (Ni) at the surface of perovskite oxides in situ has shown remarkable catalytic activity and durability towards carbon monoxide (CO) and nitric oxide (NO) oxidation and in fuel cells. In this study, for CO oxidation reaction, the catalytic capabilities of exsolved Ni nanoparticles can be further enhanced when iron (Fe) and cobalt (Co) are co-exsolved with Ni, as FeNi and CoNi alloy nanoparticles, forming mixed oxide nanoparticles. FeNi alloy nanoparticles exhibit almost ten times site activities as compared to the Ni nanoparticles, owing to the oxide layer formation which then aided the oxidation of CO. Interesting enough, the CoNi alloy nanoparticles exhibit slightly different morphological and chemical transformation due to the difference in oxidation mechanism and the degree of oxidation, which reveal greater site activities towards CO oxidation. These nanoparticles were also subjected to additional compressive strain when they expanded as a result of them being pinned to the support. These results pave the way for new approach in altering the activity of the exsolved materials for various reactions.

Mechanism of CO oxidation by oxygen in the presence of palladium(ii) bromide complexes: a quantum chemical modeling

Mechanisms of CO oxidation by oxygen in the PdBr2-LiBr-MeCN-H2O system in the absence and in the presence of iron(ii) phthalocyaninate (PcFe) as co-catalyst were studied within the framework of the density functional theory with the PBE functional. According to calculations, palladium(ii) bromide complexes most likely occur as Pd(AN)(CO)Br2 (AN is acetonitrile), Pd(CO)2Br2, and [Pd(CO)Br3]−. From the results of calculations it follows that neutral complexes Pd(AN)(CO)Br2 and Pd(CO)2Br2 can be highly catalytically active in the CO oxidation. Insertion of O2 into the Pd-H bond in the hydride complexes is the rate-limiting step of the CO oxidation reaction proceeding in the absence of PcFe as co-catalyst. Iron(ii) phthalocyaninate present in the reaction system causes a noticeable decrease in the activation energy of regeneration of the PdII complexes due to more efficient activation of O2. The oxidation of palladium hydride complexes by iron superoxophthalocyaninate can follow two routes that differ in the fashion of hydride transfer.

Double complex salts containing [Pt(NO3)6]2- anion and Rh(III) complex cations: Synthesis, structure and utilisation for preparing (Rh–Pt)/CeO2 catalysts

Three new double complex salts (DCSs) containing [Pt(NO3)6]2- anion and Rh(III) metalorganic cations [Rh(4-pic)4Cl2]2[Pt(NO3)6] (1,4-pic = 4-methylpyridine), [Rh(bpy)3]2[Pt(NO3)6]3 (2, bpy = 2,2′-bipyridiine) and [Rh(bpy)3][Pt(NO3)6](NO3)(CH3COCH3)(CH3CN)(H2O) (3) were prepared and characterised by elemental analysis and infrared spectroscopy. Crystal structures of 1 and 3 were determined using X-ray single crystal analysis. Thermal decomposition of salts 1 and 2 in various atmospheres (He, He/H2, air) was shown to yield Rh–Pt solid solutions with a Rh:Pt ratio inherited from the starting salt composition. The Rh0·67Pt0·33/CeO2 catalyst was prepared by thermal decomposition of salt 1 supported on a CeO2 surface. The catalyst was tested in a CO oxidation reaction and demonstrated full conversion of CO from about 145 °C at gas hourly space velocity of 200 000 ml g−1 h−1.

Influence of the Plasma of Pd–Ce/Porous Biomass Carbons Catalysts on the Surface Texture with Enhance Catalytic Activity Toward CO Oxidation

The porous biomass carbons (PBCs) as catalyst supports were synthesized by simple hydrothermal and carbonization method, and the surface property of PBCs were designed by plasma treatment technology. The Pd and Ce loaded TPBCs (PBCs were treated with plasma) supports were evaluated for their catalytic activity in the CO oxidation reaction. The Pd–Ce/TPBCs-20 catalyst (Conditions: CO concentration: 1 vol%, Total flow rate: 50 mL min−1, Moisture: 4 vol%) exhibited the highest catalytic activity, and the complete conversion temperature (T100) was about 20 °C for CO catalytic oxidation. Moreover, the Pd–Ce/TPBCs-20 catalyst behaved an excellent stability with the CO conversion rate in the presence of moisture, remaining higher than 90% after 24 h on stream at 20 °C. Raman, XPS, H2-TPR and O2-TPD analysis revealed that the surface oxygen-containing functional groups and defect concentration will increase with increasing plasma treatment time, which could improved Pd and Ce diffusion and Pd–O–Ce bonding interactions, resulting in increased CO catalytic activity. In addition, chitosan as the raw material for the synthesis of PBCs support, is low-cost and easy to be obtained from nature. Therefore, the Pd–Ce/TPBCs catalysts have great potential for catalytic removal of CO in practical application.

Catalytic mechanism and bonding analyses of Au-Pd single atom alloy (SAA): CO oxidation reaction

Single-atom catalysts (SACs), including metal-metal-bonded bimetallic ones named single-atom alloys (SAAs), have aroused significant interest in catalysis. In this article, the catalytic mechanism and bonding analysis of CO oxidation reaction on bimetallic gold-palladium (Au-Pd) model of single atom alloy Au37Pd1 are investigated by using quantum chemical calculations. The molecular geometries and adsorbate/substrate binding energies of CO@Au-Pd, O2@Au-Pd and CO/O2@Au-Pd configurations are identified. The core-shell structure is confirmed to be the most stable structure for Au-Pd SAA, where the Pd atom prefers to situate at the core site. Charge transfer from the Pd atom to the Au atoms has been confirmed to stabilize the structure. According to the binding energy and chemical bonding analysis, both CO and O2 prefer to bind to the Pd atom at the hex site with low coordination number. The formation of new co-adsorption species is identified, in which vertical and parallel bridging adsorptions of CO and O2 on the Au-Pd bonds are observed. CO oxidation on Au-Pd SAA is found to be feasible with low energy barriers and follows the Langmuir-Hinshewood (L-H) mechanism. Our work offers insights into the significant role of single atom of the SAAs in catalytic reactions and can provide evidence for designing new SAAs with high-performance catalytic activities.

ACTIVITY OF Pd-MnOx/CORDIERITE (Mg,Fe)2Al4Si5O18) CATALYST FOR CARBON MONOXIDE OXIDATION

Physical-chemical characteristics and activity of the Pd-MnOx-catalyst, deposited on cordierite carrier, was studied in the CO oxidation reaction. The results obtained on the catalyst Pd-MnOx-/Al–Si showed the similar activity in the CO oxidation reaction as in the case of the Pd-MnOx/CaO.2Al2O3 catalyst.

Doping Manganese Oxides with Ceria and Ceria Zirconia Using a One-Pot Sol\u2013Gel Method for Low Temperature Diesel Oxidation Catalysts

Octahedral molecular sieves (OMS-2) are an interesting form of manganese oxide with a 2 × 2 edge sharing tunnel structure and a cation positioned inside. Cryptomelane is an OMS-2 material with K+ cations within the crystalline tunnel and has been widely used in catalytic oxidation reactions, due to a mixed valency of Mn3+ and Mn4+ cations. Cryptomelane (K-OMS-2) can be modified by structural incorporation of various dopants and tunnel cations which can enhance the catalytic activity of the material. It also offers to be a promising alternative material for the low temperature emission control of combustion vehicles; particularly during cold start and low temperature conditions of diesel vehicles. In this work we used a one-pot sol–gel route to synthesize a range of manganese oxide based supports doped with Ce and CeZrO2, as alternative low temperature diesel oxidation catalysts. We have investigated the combination of manganese, ceria and zirconia in mixed oxide catalyst supports. The synthesized samples were loaded with 1 wt% Pt and their activity in the oxidation reactions of CO and C3H6, were compared with a commercial diesel oxidation catalyst with the same metal loading. The reductions in CO and C3H6 oxidation temperature T50 of 109 K and 81 K respectively was achieved compared to a commercial diesel oxidation catalyst.

CO oxidation through the formation of carboxyl intermediate on Pt(111) surface: A first principles study

The interaction of gas molecules with metal surfaces is extensively studied both theoretically and experimentally. An example of this interaction is the oxidation reaction of carbon monoxide (CO) by hydroxyl (OH) catalyszed by platinum (Pt) in the direct methanol fuel cells (DMFCs). Here, the work offers a simulation of the CO oxidation reaction by the formation of carboxyl group intermediates (COOH) based on the total energy calculation of density functional theory (DFT). The discussion here focuses on the energetics for the reaction of CO(ads) + OH(ads) → COOH(ads) and the decomposition of COOH(ads) → CO2(ads) + H(ads) on the Pt(111) surface. The calculation results show that the formation of COOH(ads) requires an energy of 0.39 eV, whereas the decomposition of COOH(ads) into CO2(ads) and H(ads) requires an activation energy of 0.14 eV. These results indicate that oxidation of CO by the COOH intermediate on Pt(111) surface is possible to occur, considering that the total energy required for the reaction is very low.

Classification of the Hysteresis Phenomena of CO Oxidation in Hydrogen Production

The study is motivated by a review of experimental and numerical evidence for the existence of bistability and hysteresis in CO oxidation on platinum group metals. In this paper, a detailed taxonomy of CO oxidation on Pd(111) is achieved by considering it as classification problem of hysteresis functions. This consideration offers a way of classifying the hysteresis behavior into several types using the mathematics of finite state automata, and in this way a through classification is achieved. The classification can provide a global framework for understanding the hysteresis behavior of CO oxidation reaction on Pd(111).

DFT calculation of electric field effect on the energy profile of the CO oxidation reaction catalyzed by Ni nanoparticles

The DFT calculations of energy profiles for the carbon monoxide oxidation reaction in the presence of Ni catalyst in the various electric fields were performed by means of the Gaussian package. In order to do that the simple computational model was suggested for the active sites on the surface of the Ni catalyst prepared by the laser electrodispersion (LED) method. The data obtained demonstrate that the energy barriers on the reaction path, which the reaction kinetics is determined by, may be reducted in the electric field by factor from 12% up to 90%. This result supports the hypothesis, that the spontaneous charge redistribution in the catalytic systems produced by the LED method may affect significantly their catalytic activity.

LaOx(OH)y supported platinum catalysts for CO oxidation: Deactivation by formation of lanthanum carbonate

Platinum catalyst for CO oxidation has been studied for decades, due to its high activity and good stability. In this work, we prepared three different lanthanum oxide or hydroxide supports (LaOx(OH)y), and deposited platinum (Pt) with 0.5 at% via an impregnation approach to synthesize Pt/LaOx(OH)y catalysts. However, we find that these catalysts perform a poor stability for the CO oxidation reaction. The fresh and used samples were comprehensively characterized by multiple techniques including power X-ray diffraction (XRD), X-ray absorption fine structure (XAFS), transmission electron microscopy (TEM), temperature-programmed reduction by carbon monoxide (CO-TPR) and thermogravimetric analysis (TGA), to demonstrate that the oxidized platinum atoms or clusters, without any component of Pt–Pt metallic bond, are highly dispersed on the surface of LaOx(OH)y. Furthermore, the as-formed lanthanum carbonate (La2O2CO3) during the exposure to ambient circumstances or in the reaction atmosphere of CO + O2, severely impair the reactivity of Pt/LaOx(OH)y. On the basis of the obtained experimental results, we have drawn a conclusion that the oxidized PtOx atoms or PtxOy clusters are the active species for CO oxidation, while the formation of lanthanum carbonate is the origin of deactivation on reactivity.

Au/SBA-15 catalyst prepared by ozone treatment and importance of negatively charged gold in CO oxidation by DRIFTS

There is a lack of consensus on the charge state of active gold species in catalytic CO oxidation reaction. Herein, Au/SBA-15 catalyst was prepared by room temperature ozone treatment. Through diffuse reflectance Fourier-transform infrared spectroscopy (DRIFTS), two different gold species, Au0 and Auδ− with CO adsorption at about 2112 cm−1 and 2077 cm−1, were observed on Au/SBA-15. In CO oxidation mixture, the 2077 cm−1 band is completely attenuated while the 2112 cm−1 band retains some intensity. CO–Auδ- bonding is weaker than that of CO–Au0, but CO–Auδ- exhibits higher reactivity towards oxygen. Ozone treatment produces AuOx nanoparticles that is not stable and decomposes to metallic Au gradually. To our best knowledge, this is the first time to identify the presence and importance of Auδ− species for “inert” SiO2 supported gold catalyst.