Trends in the CO oxidation and PROX performances of the platinum-group metals supported on ceria

Highly Effective Pt-Co/ZSM-5 Catalysts with Low Pt Loading for Preferential CO Oxidation in H2-Rich Mixture

New Pt-Co catalysts of hydrogen purification from CO impurities for fuel cells were fabricated via the deposition of monodispersed 1.7 nm Pt nanoparticles using laser electrodispersion on Co-modified ZSM-5 prepared by the Co(CH3COO)2 impregnation. The structure of prepared Pt-Co zeolites was studied by low-temperature N2 sorption, TEM, EDX, and XPS methods. The comparative analysis of samples with different Pt (0.01–0.05 wt.%) and Co (2.5–4.5 wt.%) contents on zeolites with the ratio of Si/Al = 15, 28, and 40 was performed in the CO-PROX reaction in H2-rich mixture (1%CO + 1%O2 + 49%H2 + 49%He). The synergistic catalytic action of Pt and Co on zeolite surface makes it possible to completely remove CO from a mixture with hydrogen in a wide temperature range from 50 to 150 °C; the high efficiency of designed composites with low Pt loading is maintained for a long time. The enhancement of PROX performance originates from the formation of new active sites for the CO oxidation at the Pt-Co interfaces within zeolite channels and at the surface. In terms of their activity, stability, and selectivity, such composites are significantly superior to known supported Pt-Co catalysts.

Promotional Effect of H2 Pretreatment on the CO PROX Performance of Pt1/Co3O4: A First-Principles-Based Microkinetic Analysis

Atomic Pt studded on cobalt oxide is a promising catalyst for CO preferential oxidation (PROX) dependent on its surface treatment. In this work, the CO PROX reaction mechanism on Co₃O₄ supported single Pt atom is investigated by a comprehensive first-principles based microkinetic analysis. It is found that as synthesized Pt₁/Co₃O₄ interface is poisoned by CO in a wide low temperature window, leading to its low reactivity. The CO poisoning effect can be effectively mitigated by a H₂ prereduction treatment, that exposes Co ∼ Co dimer sites for a noncompetitive Langmuir-Hinshelhood mechanism. In addition, surface H atoms assist O₂ dissociation via "twisting" mechanism, avoiding the high barriers associated with direct O₂ dissociation path. Microkinetic analysis reveals that the promotion of H-assisted pathway on H₂ treated sample helps improve the activity and selectivity at low temperatures.

Reactivity of Pd-MO2 encapsulated catalytic systems for CO oxidation

In this study, we present an investigation aimed at characterizing and understanding the synergistic interactions in encapsulated catalytic structures between the metal core (i.e., Pd) and oxide shell (i.e., TiO2,...

The Mitigation of CO Present in the Water–Gas Shift Reformate Gas over IR-TiO2 and IR-ZrO2 Catalysts

CO hydrogenation and oxidation were conducted over Ir supported on TiO2 and ZrO2 catalysts using a feed mimicking the water–gas shift reformate stream. The influence of the support interaction with Ir and the catalysts’ redox and CO chemisorption properties on activity and selectivity were evaluated. Both catalysts oxidised CO to CO2 in the absence of H2, and a conversion of 70% was obtained at 200 °C. For the CO oxidation in the presence of H2 over these catalysts, the oxidation of H2 was favoured over CO due to H2 spillover occurring at the active metal and support interface, resulting in the formation of interstitials catalysed by Ir. However, both catalysts showed promising activity for CO hydrogenation. Ir-ZrO2 was more active, giving 99.9% CO conversions from 350 to 370 °C, with high selectivity towards CH4 using minimal H2 from the feed. Furthermore, results for the Ir-ZrO2 catalyst showed that the superior activity compared to the Ir-TiO2 catalyst was mainly due to the reducibility of the support and its interaction with the active metal. Controlling the isoelectric point during the synthesis allowed for a stronger interaction between Ir and the ZrO2 support, which resulted in higher catalytic activity due to better metal dispersions, and higher CO chemisorption capacities than obtained for the Ir-TiO2 catalyst.

Temperature reversible synergistic formation of cerium oxyhydride and Au hydride: a combined XAS and XPDF study

In situ studies on the physical and chemical properties of Au in inverse ceria alumina supported catalysts have been conducted between 295 and 623 K using high energy resolved fluorescence detection X-ray absorption near edge spectroscopy and X-ray total scattering. Precise structural information is extracted on the metallic Au phase present in a 0.85 wt% Au containing inverse ceria alumina catalyst (ceria/Au/alumina). Herein evidence for the formation of an Au hydride species at elevated temperature is presented. Through modelling of total scattering data to extract the thermal properties of Au using Grüneisen theory of volumetric thermal expansion it proposed that the Au Hydride formation occurs synergistally with the formation of a cerium oxyhydride. The temperature reversible nature, whilst remaining in a reducing atmosphere, demonstrates the activation of hydrogen without consumption of oxygen from the supporting ceria lattice.

Recent advances in synergistic effect promoted catalysts for preferential oxidation of carbon monoxide

We reviewed recent advances in catalysts for PROX with emphasis on synergistic effects that contribute to enhanced catalytic performance.

Reduced SrTiO3-supported Pt-Cu alloy nanoparticles for preferential oxidation of CO in excess hydrogen

Activity and long-term stability of oxide-metal heterostructure catalysts can be engineered through tuning the oxygen storage capacity (OSC) of the support and careful control of the composition of the supported metal nanoparticle. In this work, we probe these two factors for microwave-synthesized PtCu alloy nanoparticles supported on reduced-SrTiO3. The heterostructures are tested for their activity towards preferential CO oxidation in the presence of H2 at typical operating temperatures used for polymer electrolyte membrane fuel cells (PEMFCs). Through controlled temperature programmed reduction/temperature programmed oxidation (TPR/TPO) experiments, we show that the OSC of the support can be enhanced through heavy surface reduction of SrTiO3. Adsorption-desorption experiments establish the strikingly different CO adsorption behavior over monometallic Pt and PtCu alloy nanoparticles. Through detailed catalytic studies, we establish a trend in the selectivity and stability of CO conversions over the PtCu alloy catalysts that can indeed be tuned by varying the PtCu composition in a facile microwave synthesis.

Effect of Hydrazine Pretreatment on the Activity, Stability and Active Sites of Cobalt Species for Preferential Oxidation (PROX) of CO in H2-Rich Stream

The as-prepared (Co3O4) and hydrazine-treated (Co3O4(H)) cobalt catalysts were prepared using the precipitation method and evaluated at a temperature range of 40–220 °C for preferential oxidation (PROX) of CO in excess hydrogen. An improved surface reducibility with smaller crystallite size was noted on hydrazine-treated cobalt species (i.e., Co3O4(H) catalyst), which indicates some surface transformation. This finding correlates with the surface roughness formation (as depicted by scanning electron microscope (SEM) and transmission electron microscope (TEM) data), which was further confirmed by an increase in the Brunauer–Emmett–Teller (BET) surface area. The mesoporous structure of the Co3O4(H) catalyst remained intact, as compared to that of the Co3O4 catalyst. Interestingly, the in situ treatment of the standalone Co3O4(H) catalyst decreased the maximum CO conversion temperature (T100%) from 160 °C (over Co3O4) to 100 °C, with good selectivity. The Co3O4(H) catalyst showed good stability, with approximately 85% CO conversion at 100 °C for 21 h, as compared to a faster deactivation of the Co3O4 catalyst. However, the Co3O4(H) catalyst was unstable in both CO2 and the moisture environment. Based on the evaluation of spent hydrazine-treated (CoO(H)) cobalt catalyst, the high PROX activity is associated with the formation of Co3+ species as confirmed by X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), and temperature-programmed reduction (TPR) data.

Identification of a flattened Pd–Ce oxide cluster as a highly efficient catalyst for low-temperature CO oxidation

An improved deposition method was employed to prepare a Pd/CeO₂ catalyst, which exhibited highly efficient activity in low-temperature CO oxidation (LTO).

CO oxidation over MOx (M = Mn, Fe, Co, Ni, Cu) supported on SmMn2O5 composite catalysts

The ability to oxidize CO at relatively low temperature is barely satisfactory for pure SmMn₂O₅ (SMO) catalysts.

Probing the thermal-enhanced catalytic activity of CO oxidation over Pd/OMS-2 catalysts

An elevating calcination temperature within 500 °C lead to the spill-over of the palladium, the increase of surface palladium abundance and catalytic activity. Phase transformation of OMS-2 and deactivation of the catalyst happened above 500 °C.

Solution Combustion Synthesis of Nanoscale Materials

Solution combustion is an exciting phenomenon, which involves propagation of self-sustained exothermic reactions along an aqueous or sol-gel media. This process allows for the synthesis of a variety of nanoscale materials, including oxides, metals, alloys, and sulfides. This Review focuses on the analysis of new approaches and results in the field of solution combustion synthesis (SCS) obtained during recent years. Thermodynamics and kinetics of reactive solutions used in different chemical routes are considered, and the role of process parameters is discussed, emphasizing the chemical mechanisms that are responsible for rapid self-sustained combustion reactions. The basic principles for controlling the composition, structure, and nanostructure of SCS products, and routes to regulate the size and morphology of the nanoscale materials are also reviewed. Recently developed systems that lead to the formation of novel materials and unique structures (e.g., thin films and two-dimensional crystals) with unusual properties are outlined. To demonstrate the versatility of the approach, several application categories of SCS produced materials, such as for energy conversion and storage, optical devices, catalysts, and various important nanoceramics (e.g., bio-, electro-, magnetic), are discussed.

Pd/zeolite-based catalysts for the preferential CO oxidation reaction: ion-exchange, Si/Al and structure effect

A screening of Pd/zeolite-based catalysts in the PrOx-CO reaction in H₂-rich streams was performed using zeolites with different cations (H⁺, Na⁺ and Cs⁺) prepared by ion exchange and framework type (MFI and FAU).

Ni on the CeO2(110) and (100) surfaces: adsorption vs. substitution effects on the electronic and geometric structures and oxygen vacancies

We report density functional theory (DFT) calculations of the interactions of both Ni adsorbate and substitutional dopant with the ceria (110) and (100) surfaces to explain the origin of the activity of Ni/ceria catalysts.

A low-temperature method for measuring oxygen storage capacity of ceria-containing oxides

Addition of Pt/Al₂O₃ to a ceria-containing oxide allows studying oxygen storage capacity at lower temperatures. The advantage is achieved through separation of functions of oxygen storage/release and CO oxidation.

Sensitivity of CO oxidation toward metal oxidation state in ceria-supported catalysts: an operando DRIFTS-MS study

CeO₂ and Rh/CeO₂ show CO to CO₂ conversion according to the input gas mixture, independent of the state of the catalyst powder. Pt/CeO₂ demonstrates additional dependence on the initial state of the catalyst (oxygen coverage/oxidation state).

Low-temperature catalytic oxidation of CO over highly active mesoporous Pd/CeO2–ZrO2–Al2O3catalyst

Addition of zirconium and aluminum into Pd/CeO₂led to an increase of surface atomic ratios of Ce³⁺/Ce⁴⁺andO_adsorbed/O_lattice, pore volume, ratios and size of mesopores, catalytic activity, as well as decrease of particle size,E_aandT₁₀₀(60 °C).