Bichun Huang

Effects of cerium on the selective catalytic reduction activity and structural properties of manganese oxides supported on multi-walled carbon nanotubes catalysts

Abstract A series of manganese and cerium oxides supported on multi-walled carbon nanotubes (MWCNTs) catalysts for low-temperature NH 3 selective catalytic reduction (SCR) of NO x were prepared by the pore volume impregnation method. The SCR activity of Mn-Ce/MWCNTs catalysts was compared with that of Mn/MWCNTs catalyst. The effects of Ce were characterized by transmission electron microscopy, N 2 adsorption-desorption, H 2 temperature-programmed reduction, X-ray photoelectron spectroscopy and X-ray powder diffraction. The results show that the addition of cerium oxides could improve the SCR activity of Mn/MWCNTs catalysts. Mn-Ce/MWCNTs catalyst with a Ce/Mn ratio of 0.6 was found to have the highest activity. The addition of cerium oxides enhanced the dispersion of metal oxides on the MWCNTs. It could also increase the specific surface area and total pore volume, and decrease the average pore size of the catalysts. Ce would improve the concentration of oxygen and the valence of manganese. Furthermore, from the XRD results, it was obvious that the crystalline MnO x disappeared because of the introduction of Ce to the catalyst. MnO x mainly existed in an amorphous state or microcrystal structure in the Mn-Ce/MWCNTs catalysts. CeO 2 was found to be the main phase for CeO x .

Low-temperature SCR of NOx by NH3 over MnOx/SAPO-34 prepared by two different methods: a comparative study

ABSTRACT The low-temperature selective catalytic reduction (SCR) of NOx is a promising technology for removing NOx from flue gases. However, the vulnerability of Mn-based catalysts to SO2 and H2O poisoning makes them unsuitable for industrial application. Herein, catalysts based on the MnOx/SAPO-34 catalysts were prepared by conventional impregnation and an improved molecularly designed dispersion method for use in the low-temperature SCR. The improved molecularly designed catalyst containing 20 wt% of MnOx exhibited high low-temperature NH3-SCR activity. Nearly 90% of the NOx was converted exclusively to N2 at 160°C using this catalyst. The structure and morphological analyses of the catalyst showed that the amorphous MnOx was well dispersed on the surface of the support. The reasons for the high performance of the catalysts were ascertained using surface N2 adsorption, XPS, H2-TPR and NH3-TPD. The results of these analyses indicated that high specific surface area and the redox capability, of the abundant Mn4+ and Mn3+ species, coupled with the surface chemisorbed oxygen and strong acid sites had a significant effect on the SCR reaction. In addition, the effects of SO2 and H2O on activity of the catalysts were also investigated and it was found that the highly dispersed 20 wt% MnOx/SAPO-34 catalyst exhibited better SO2 poisoning resistance than the other impregnated catalysts.

Synergistic Effect of a Carbon Black Supported PtAg Non‐Alloy Bimetal Nanocatalyst for CO Preferential Oxidation in Excess Hydrogen

Carbon black (CB) supported PtAg non‐alloy bimetal catalysts were prepared by incipient wetness impregnation and evaluated for CO preferential oxidation in excess H2 (PROX). PtAg/CB catalysts exhibited an evident synergistic effect. The catalyst support selection is crucial to the synergistic effect. X‐ray diffraction (XRD), transmission electron microscopy (TEM), and scanning TEM energy dispersive X‐ray analysis (STEM‐EDX) characterization indicates no alloy was formed over the PtAg/CB catalyst after activation in H2 at 500 °C for 2 h. However, temperature‐programmed reduction (TPR) and XRD data evidenced strong interactions between platinum and silver, as a result of their simultaneous reduction and high temperature activation. The PtAg interactions result in high catalytic performance and the synergistic effects. This is another example of model catalyst research translating to real world catalysis. PtAg non‐alloy catalysts may also be effective in eliminating or alleviating catalyst poisoning by CO‐like intermediates in direct liquid fuel cells.

Promotion effect of adsorbed water/OH on the catalytic performance of Ag/activated carbon catalysts for CO preferential oxidation in excess H2

Abstract Activated carbon (AC) supported silver catalysts were prepared by incipient wetness impregnation method and their catalytic performance for CO preferential oxidation (PROX) in excess H 2 was evaluated. Ag/AC catalysts, after reduction in H 2 at low temperatures (≤200 °C) following heat treatment in He at 200 °C (He200H200), exhibited the best catalytic properties. Temperature-programmed desorption (TPD), X-ray diffraction (XRD) and temperature-programmed reduction (TPR) results indicated that silver oxides were produced during heat treatment in He at 200 °C which were reduced to metal silver nanoparticles in H 2 at low temperatures (≤200 °C), simultaneously generating the adsorbed water/OH. CO conversion was enhanced 40% after water treatment following heat treatment in He at 600 °C. These results imply that the metal silver nanoparticles are the active species and the adsorbed water/OH has noticeable promotion effects on CO oxidation. However, the promotion effect is still limited compared to gold catalysts under the similar conditions, which may be the reason of low selectivity to CO oxidation in PROX over silver catalysts. The reported Ag/AC-S-He catalyst after He200H 2 00 treatment displayed similar PROX of CO reaction properties to Ag/SiO 2 . This means that Ag/AC catalyst is also an efficient low-temperature CO oxidation catalyst.

The graphitic carbon strengthened synergetic effect between Pt and FeNi in CO preferential oxidation in excess hydrogen at low temperature

A variety of PtFeNi catalysts supported on carbon materials have been prepared and tested for CO preferential oxidation (PROX) in excess hydrogen. 100% O2 and CO conversions have been achieved over carbon black (CB) and carbon nanotube (CNT) supported PtFeNi catalysts at room temperature in a feed gas containing 1% CO, 0.5% O2 (volume ratio) and H2 balance gas. N2 adsorption, temperature-programmed desorption (TPD) and transmission electron microscopy (TEM) studies indicate that the carbon textural properties and surface chemistry determine the catalyst particle size distribution and mean size; but the mean particle size does not have a great influence on the catalytic performance within the investigated particle size range. X-ray diffraction (XRD), resistance measurements and the designed catalytic reaction results reveal the ability of graphitic carbon to capture and shuttle electrons from the noble metal to spatially different sites in the FeNi species through the π–π network, enables the indirect interactions between Pt and the FeNi species, leading to a strengthened synergistic effect, enhancing the CO oxidation activity at room temperature, increasing the Pt utilization efficiency, and apparently decreasing the Pt loading level.