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Calcined Na-ZSM-5 zeolite was directly reacted with the chloroauric acid solution in different concentrations and pH for gold loading process. The synthesized Au/ZSM-5 catalyst was then characterized using XRD, BET, SEM, TEM and EDS techniques. In order to evaluate its catalytic activity, effect of temperature on CO conversion was investigated.

This review summarizes recent studies on the catalytic CO oxidation on Iridium(111) surfaces. This was investigated experimentally under ultrahigh vacuum (UHV) conditions using mass spectroscopy to detect gaseous products and photoelectron emission microscopy (PEEM) to visualize surface species. The underlying reaction–diffusion system based on the Langmuir–Hinshelwood mechanism was analyzed numerically.

The existence of bistability for this surface reaction was shown in experiment. For the first time the effect of noise on a bistable surface reaction was examined. In a surface science experiment the effects on product formation and the development of spatio-temporal patterns on the surface were explored.

Steady state CO₂ rates were measured under constant flux of the CO + O mixture as a function of sample temperature (360 K < T < 700 K) and gas composition, characterized by the molar fraction of CO in the feed gas (0 ≤ Y ≤ 1). The reaction reveals bistability in a limited region of Y and T. A rate hysteresis with two steady state rates was observed for cycling Y up and down, one of high reactivity (upper rate, oxygen covered surface) and one of low reactivity (lower rate, CO covered surface). The position of the hysteresis loop shifts to higher Y values and decreases in width with increasing temperature. For small CO content in the feed gas the CO₂ rate is proportional to Y^3/2. At 500 K extremely slow Y cycling measurements (about 100 hours per direction) were done and showed that bistability still exists and no slowly changing transients were observed. The requirements for the speed with which experiments can be executed without producing experimental artifacts were explored. Since over-sampling alters the measured hysteresis loop, a maximum rate for changing the gas composition in Y cycling experiments was determined.

The influence of noise on the reaction rates and the formation of spatio-temporal patterns on the surface was explored by superposing noise of Gaussian white type on Y and on T. Noisy Y (deviation Δ Y) represents multiplicative and additive noise, noisy T (deviation Δ T) multiplicative noise only. Noisy T enters the reaction via the rate-determining step, the observed CO₂ rates become noisy for low temperatures (around 420 K) when the surface is dominantly oxygen covered (CO + O reaction step is rate-limiting) and for higher temperatures (around 500 K) when the surface is dominantly CO covered (CO desorption step is rate-limiting).

The effect of noisy Y was examined for a sample temperature of 500 K and is dependent on the selected average gas composition. In the regions with one steady state CO₂ rate (outside the hysteresis) the recorded rates were noisy. The probability distribution of the rates is Gaussian shaped for the upper rate (below hysteresis) and asymmetric for the lower rate (above hysteresis). For large noise strength bursts, short-time excursions to and above the upper rate, were observed.

Inside the hysteresis small noise made the steady state rates noisy, but above a Y-dependent Δ Y transients from the locally stable to the globally stable rate branch were observed. These transients take up to several ten thousand seconds and become faster with increasing noise. For larger Y noise strength bursts and switching between both steady state rates were detected.

Photoelectron emission microscopy (PEEM) was done to visualize spatio-temporal adsorbate patterns on the surface as expected from the observations in the CO₂ rate measurements. CO- and oxygen-covered regions on the Ir(111) surface are visible in PEEM images as gray and black areas as a consequence of their work function contrast. Islands of the adsorbate, corresponding to the globally stable branch, are formed in a background of the other one. The long transient times are the result of the extremely slow domain wall motion of these islands (around 0.05 μm s^-1). In the hysteresis region CO oxidation on Iridium(111) surfaces is dominated by domain formation and wall motion for small to moderate noise strength. The island density increases with noise, but the wall velocity is independent of applied Δ Y. For larger noise amplitudes, fast switching between oxygen- and CO-dominated surfaces is observed as well as nucleation and growth of the minority phase in the majority phase.

In the numerically analyzed reaction–diffusion system all parameters were taken from the experiment. Modeling the reaction–diffusion system shows qualitative up to quantitative agreement with the experimental observations. The length scale for the modeling grid is determined from wall velocity seen in the experiments.

Nanocrystalline cerium oxide (CeO₂) particles prepared by the novel two-stage precipitation method were used for the catalysis of CO oxidation. Firstly, two shapes, i.e. particulate (P-) and needle-like (N-), CeO₂ nanoparticles were formed via proposed temperature-arranged routes. The crystalline structure, morphology, particle size, and surface area of samples were characterized by using XRD, TEM, HRTEM, and BET techniques. Furthermore, the morphological effect of the CeO₂ samples on the catalytic activity of CO oxidation was investigated. From the experimental results, it indicated that the prepared samples were all nonporous and fcc-structured CeO₂. The CeO₂ particles, as precipitating at 90°C for 5 min and then aging at 90°C, were particulate, whereas they were needle-like by aging at 0°C. The CO oxidation reaction showed that the catalytic activity of N-CeO₂ nanoparticles was higher than that of P-CeO₂, attributing from the exposed higher-energy {100} and {110} facets for N-CeO₂ nanoparticles. Moreover, the calcined samples with higher degree of crystallinity showed further promotion in catalytic activity. It was also worthy to note, that by replacing the CeO₂ catalyst by Pd/CeO₂, a large increase in the CO conversion was found, especially catalyzed by Pd/N-CeO₂.

The effects of pretreating atmospheres (H₂, O₂ and Ar) on the activity for CO oxidation and Pd dispersion of Pd/Pr₆O₁₁ catalyst were investigated. The result shows after the Pd/Pr₆O₁₁ catalyst was pretreated by hydrogen or oxygen at 550°C, its catalytic activity for CO oxidation can obviously increase, and the activity of H₂-pretreated catalyst is superior to that of O₂-pretreated catalyst, which is attributed to an increase of Pd dispersion. The catalyst pretreated by Ar behaves the worst catalytic activity for CO oxidation. The results of CO pulse, CO chemisorption and in situ DRIFT testing indicate that the surface species (hydroxyl species or active oxygen species) generated during pretreating processes can prevent Pd particles from immigrating and sintering, resulting in an increase of the Pd dispersion on the surface of support.

Gold supported hydroxyapatite (HA) and calcium deficient hydroxyapatite (CDHA) was studied for the room temperature CO oxidation. Nanostructured gold catalyst has been prepared by deposition precipitation method, whereas HA was synthesized by microwave synthesis. Inorder to understand the influence of surface properties of HA, support HA was synthesized with different Ca/P ratios (1.67, 1.62, 1.57, 1.534 and 1.5). The gold supported catalysts were characterized by XRD, BET, ICP-OES and TEM. Typical results indicate that gold supported 1.57 HA shows higher activity compared to other HA catalysts (1.67, 1.62, 1.534 and 1.5) which may be due to the presence of optimum number of acidic and basic sites.

A facile strategy is described for general synthesis of MCo₂O₄@CeO₂ ($\mathrm{\text{M}}=\mathrm{\text{Ni}}$, Cu, Zn, Mn) core@shell nanospheres. First, uniform M,Co–glycerate were prepared and served as precursor to produce MCo₂O₄ spheres by calcination, followed by a reflux process to obtain MCo₂O₄@CeO₂ core@shell spheres. As expected, due to the synergetic effect at the interface between the two components, most of the as-prepared MCo₂O₄@CeO₂ core@shell spheres exhibited enhanced catalytic activities toward CO oxidation compared with the corresponding MCo₂O₄ spheres and CeO₂ nanoparticles.

In this paper, two Au/CeO₂ catalytic systems have been fabricated through the synthesis of porous CeO₂ from Ce-BTC MOFs nanorod and nanobundle precursors by thermal annealing, and the subsequent Au loading. Significantly, the catalytic activity of Au/CeO₂ nanorods is higher than that of bare CeO₂ and even Au/CeO₂ nanobundles for both CO oxidation and 4-nitrophenol reduction. The remarkably enhanced performance of Au/CeO₂ nanorods can be attributed to the unique porous structure, high surface area, abundant oxygen vacancies on the surface of CeO₂, and the synergistic effect between gold and ceria.

In this paper, the oxidation mechanism of carbon monoxide (CO) on two-dimensional porphyrin sheet within a single cobalt atom (Co-TDPs) was studied by density functional theory with dispersion (DFT-D). The stability of Co-TDPs at different temperatures was verified by first-principle molecular dynamics simulations. Absorption energies of reactant and product to anchor to the Co–N₄ site showed CO and O₂ adsorption to be stronger than the CO₂ adsorption. In addition, the Langmuir–Hinshelwood, Eley–Rideal (ER), and ter-molecular Eley–Rideal (TER) mechanisms were used to investigate the reaction mechanisms of CO oxidation on Co-TDPs. The Langmuir–Hinshelwood (LH) and ER mechanisms were feasible reaction profiles of CO oxidation because of their smaller energy barrier. The results suggested that the Co-TDPS was acting as a catalyst for CO oxidation in the mild condition.

The flower-like Cu₂O nanostructures were hydrothermally synthesized without using any template or surfactant. The influences of hydrothermal temperature, reaction time and reactants concentrations on the growth of nanostructures were investigated in detail. The samples were characterized by scanning electron microscope (SEM) and X-ray powder diffraction (XRD). Cu₂O crystals with different shapes, i.e., flower-like (F-product) cubic box (CB-product) and cubic box with holes in each face (CBH-product), were synthesized by controlling the synthesis parameters and explored for CO catalytic oxidation. It was found that F-product showed higher catalytic than others.