Carbon Monoxide In Hydrogen-rich Stream Research Articles

Synergistic effect of platinum single atoms and nanoclusters for preferential oxidation of carbon monoxide in hydrogen-rich stream

Despite the maximum atom-utilization efficiency and remarkable activity of single-atom catalysts, further improvement of catalytic activity can be obtained by the synergistic effect of single atoms and nanoclusters in some catalytic systems. Herein, CeFeOx-supported Pt single atoms coupling with subnanometric clusters (Pt1-Ptn) structures are developed via a facile strategy. They are applied as the highly efficient catalysts for the preferential oxidation of CO in H2-rich stream (CO-PROX), which achieve complete elimination of CO at low temperature of 50 °C, with a wide operating temperature window and extraordinary stability for over 500 h without noticeable deactivation. The exceptional performance is attributed to the synergistic effect of distinctive Pt1-Ptn structures, which couple the benefits of Pt single atoms and subnanometric clusters in a remarkable way. The disadvantages of single Pt species catalysts, such as sensibility to strong adsorption of CO or reduced lattice oxygen reactivity due to excessive coordination, can be well mitigated. The results of detailed characterizations and density functional theory calculations confirm that the unique structures possess moderate adsorption strength for CO and create abundant active interfacial oxygen species, because of the absence of bulk metallic Pt0 and appropriate coordination to lattice oxygen, which synergistically facilitate the catalytic performance.

Active Pt/CeO2 catalysts prepared by an alcohol-reduction process for low-temperature CO-PROX reaction

Pt/CeO2 catalysts were prepared with 0.5 and 1 wt% of Pt loadings by an alcohol-reduction process using a solution of ethylene glycol and water as a reducing agent and solvent. The obtained catalysts were characterized by energy-dispersive X-ray spectroscopy, X-ray diffraction, and transmission electron microscopy. Transmission electron micrographs showed Pt nanoparticles with average sizes of 2.2 and 2.4 nm for Pt content of 0.5 and 1 wt%, respectively. The preferential oxidation of carbon monoxide in hydrogen-rich stream (CO-PROX reaction) was studied in the temperature range of 25–150 °C. Pt/CeO2 catalysts showed maximum CO conversions in the range of 80–98% and CO2 selectivity in the range of 50–70% at 50 °C.

Au/TiO2 catalysts prepared by borohydride reduction for preferential CO oxidation at near-ambient temperature

Abstract Au nanoparticles were prepared in solution using HAuCl4.3H2O as Au precursor, sodium citrate as stabilizing agent and sodium borohydride as reducing agent. The influence of synthesis parameters such as BH4:Au and Citrate:Au ratios were studied. In a further step, the stabilized Au nanoparticles were supported on TiO2 with different Au loadings (wt%). The resulting Au/TiO2 catalysts were characterized by Energy-dispersive X-ray spectroscopy, X-ray diffraction and Transmission Electron Microscopy and tested for the preferential oxidation of carbon monoxide in hydrogen-rich stream. Au nanoparticles stabilized in solution were obtained with sizes in the range of 3-4 nm. After supported on TiO2, the Au nanoparticles size did not change and the Au/TiO2 catalysts exhibited excellent performance and stability in the temperature range of 20 - 50°C.

Nanosized Au Catalysts Supported on Mg(OH)<sub>2</sub>-CeO<sub>2</sub> for Preferential Oxidation of CO in Hydrogen Stream

Preferential oxidation of carbon monoxide in the presence of hydrogen (PROX) is a promising method to remove CO from a hydrogen-containing gas mixture. Nanosized gold catalyst supported on CeO2 and modified with Mg(OH)2 was used for preferential oxidation of carbon monoxide in hydrogen-rich stream in this study. Mg(OH)2 was added on CeO2 by incipient-wetness impregnation. Au was loaded on Mg(OH)2-CeO2 by deposition-precipitation method. PROX reaction was carried out in a continuous flow, fixed bed reactor. CO/O2 feed ratio was fixed at 1 to magnify the difference of various catalysts. The catalysts were characterized by N2 sorption, TEM, HR-TEM and XPS. Mg(OH)2 formed a thin layer on the surface of CeO2. CeO2 was in the crystalline phase and Mg(OH)2 was amorphous. Au particles were homogeneously dispersed on the support with a size of 2 - 5 nm. Using CeO2 as a support could increase the dispersion of Mg(OH)2 and thus increase the interaction between Au and Mg(OH)2. Adding Mg(OH)2 on Au/CeO2 could suppress H2 oxidation and therefore increase CO oxidation activity.

Preparation of Au/TiO2 by a facile method at room temperature for the CO preferential oxidation reaction

A simple strategy was used to prepare Au/TiO2 catalyst at room temperature. Au nanoparticles were initially prepared in solution using HAuCl4.3H2O as Au precursor, sodium citrate as stabilizing agent and sodium borohydride as reducing agent. The preformed Au nanoparticles were further supported on TiO2 and the resulting solid material was characterized by Energy-dispersive X-ray spectroscopy, X-ray diffraction and Transmission Electron Microscopy and tested for the preferential oxidation of carbon monoxide in hydrogen-rich stream (CO-PROX reaction). The obtained Au/TiO2 catalyst consisted of Au nanoparticles with an average size of ~ 4 nm and showed excellent catalytic performance in the 20-50 °C low-temperature range. In particular, at 40 °C a CO conversion of 99.5% and CO2 selectivity of 45% were obtained using an O2/CO ratio of 2 (1 vol% CO, λ = 4) and 97 vol% H2 in the feed gas stream (GHSV = 15,000 mL gcat−1 h−1).

Preparation of Au/TiO2 Catalyst by a Liquid-Phase Reduction Method for Preferential Oxidation of Carbon Monoxide in a Hydrogen Rich-Stream (CO-PROX reaction)

Au nanoparticles supported on TiO2 were prepared by a liquid-phase reduction method using HAuCl4.3H2O as the Au precursor, TiO2 as the support, a solution of ethylene glycol/water as solvent and reducing agent and sodium citrate as reducing agent and stabilizer. The Au/TiO2 catalysts were prepared using different routes and characterized by Energy-dispersive X-ray spectroscopy, X-ray diffraction and Transmission Electron Microscopy and tested for preferential oxidation of carbon monoxide in hydrogen-rich stream (CO-PROX reaction). The way that the Au precursor, the TiO2 support and the sodium citrate is added to the ethylene glycol/water solution strongly influences the Au nanoparticle sizes and the catalytic activity of the obtained materials.

Superior preferential oxidation of carbon monoxide in hydrogen-rich stream under visible light irradiation over gold loaded hedgehog-shaped titanium dioxide nanospheres: Identification of copper oxide decoration as an efficient promoter

Gold nanoparticles loaded on the special three-dimensional urchin-like micro/nano hierarchical TiO2 microspheres, with CuO layer modification, are performed for the CO preferential oxidation in H2-rich stream at room temperature under visible light irradiation or not. It is found that the suitable outer decoration of CuO in TiO2 microspheres can obviously improve the catalytic activity of Au/TiO2, and adding visible light can further promote the performance. Based on the characterizations of catalysts, it is proposed that the CuO layer distributed on the shell of TiO2 urchin-like microspheres can enhance the electron transfer among Au, TiO2 and CuO sites to drive the increase in surface electron densities of Au and support sites induced by both the localized surface plasmon resonance of Au nanoparticles and the photo-excitation of CuO under visible light irradiation, resulting in the adsorptions and activations of CO and O2. Therefore, as a synactic result of its unique band gap relation, its unique electron property and its morphologic effect, the novel CuO modified TiO2 support not only enhances the microstrain itself on the stabilization of the size of Au nanoparticles, but more importantly also reinforces the electron interaction between support and Au sites.

Preferential Oxidation of Carbon Monoxide in Hydrogen Stream over Au/MgOx−TiO2 Catalysts

A series of Au/MgOx−TiO2 with various Mg/Ti molar ratios was prepared to study its catalytic activity for preferential oxidation of carbon monoxide in hydrogen-rich stream (PROX). An incipient wetness impregnation method was used to prepare the MgOx−TiO2 support, using aqueous solutions of Mg(NO3)2 on TiO2 calcined at 300 °C. A deposition−precipitation (DP) method was utilized to prepare Au/MgOx−TiO2, using HAuCl4 as the starting material. Au/MgOx and Au/TiO2 were also included for comparison. Investigation was carried out to study the effect of Mg/Ti molar ratio on the catalytic properties of gold supported catalysts. The catalysts were characterized by inductively couple plasma-mass spectrometry, X-ray diffraction, transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy. TEM results revealed the presence of nanosized gold particles and narrow particle size distribution on all the catalysts. MgOx was deposited on the TiO2 surface in the form of thin islands without definite shape. Mg...

Selective oxidation of carbon monoxide in hydrogen-rich stream over Cu-Ce/γ-Al2O3 catalysts promoted with cobalt in a fuel processor for proton exchange membrane fuel cells

Cu-Ce/γ-Al 2 O 3 catalysts promoted with cobalt are tested for the low-temperature selective oxidation of carbon monoxide (CO) in excess hydrogen, as produced by a fuel processor for proton exchange membrane fuel cells (PEMFCs). A small addition (0.2 wt.%) of Co to Cu-Ce/γ-Al 2 O 3 leads to a large increase in the activity for selective CO oxidation. When either CO 2 (13 vol.%) or H 2 O (10 vol.%) is present in the reformed gas feed, both Cu-Ce/γ-Al 2 O 3 and Cu-Ce-Co/γ-Al 2 O 3 show a decrease in CO oxidation activity at low temperatures, especially, under 200 °C. Compared with Cu-Ce/γ-Al 2 O 3 , however, Cu-Ce-Co/γ-Al 2 O 3 gives higher resistance to CO 2 and H 2 O. There also exists a temperature window at 210–225 °C that corresponds to the conversion of 99.9% CO. From stability tests and temperature-programmed (TPD) desorption studies of CO 2 /H 2 O, it is concluded that the main cause for the decrease in catalytic activity with CO 2 and H 2 O in the feed is due to competitive adsorption of CO and CO 2 as well as to the blockage of the active sites by water vapor at low reaction temperatures.