Zhicheng Tang

Roughness evolution of ZrO2 thin films grown by reactive ion beam sputtering

A series of zirconium dioxide films were grown on rough borosilicate crown glass substrates with reactive ion beam sputtering technique. The evolution of the surface roughness was studied in the smoothing and roughening growth regimes using atomic force microscopy. By quantitative analysis of surface morphology, the interface width of the growth fronts was found to have a minimum during the deposition process. Dynamic scaling was observed for thicker films; the roughness exponent was found to be in the range of 0.7–0.9 and the growth exponent at approximately 0.4.

Influence of the pore structure of CeO2 supports on the surface texture and catalytic activity for CO oxidation

In this paper, three kinds of CeO2 nano-materials with different pore structures, i.e., mesoporous, microporous and nanoparticle CeO2, were synthesized. Mesoporous CeO2 (meso-CeO2) and microporous CeO2 (micro-CeO2) were prepared by adopting the mesoporous silica KIT-6 and microporous high silica ZSM-5 (Si/Al = 344.1) as templates, respectively. CeO2 nanoparticles (nano-CeO2) were synthesized by precipitation method. The palladium loaded meso-CeO2, micro-CeO2 and nano-CeO2 supports were evaluated for their catalytic activity in the CO oxidation reaction. The Pd/meso-CeO2 exhibited the highest catalytic activity, and the complete conversion temperature (T100) was about 50 °C for the CO oxidation. According to the analysis, the meso-CeO2 support has a mesoporous structure, large BET surface area and small particle size. At the same time, the Pd/meso-CeO2 catalyst has a large number of active surface oxygen species, Ce3+ cationic species and Pd4+ cationic species. These above characteristics of Pd/meso-CeO2 were relatively conducive to the catalytic oxidation of CO.

Influence of pore structures of a carbon support on the surface textures of a CO oxidation catalyst

In this paper, three kinds of carbon materials, i.e., carbon spheres (non-C), microporous carbon (micro-C) and mesoporous carbon (meso-C) were synthesized. Micro-C and meso-C were prepared by adopting the microporous low silica ZSM-5 and mesoporous silica KIT-6 as templates, respectively and non-C was prepared by a hydrothermal route. The palladium loaded non-C, micro-C and meso-C supports were prepared by an impregnation method, and the catalysts were applied for CO oxidation. The Pd/meso-C exhibited the highest catalytic activity because the meso-C support had a well-ordered mesoporous structure, large BET surface area, porous channels and higher dispersion of Pd nanoparticles. By adjusting the promoter type and content, calcined temperature, the optimal prepared conditions of the catalyst were achieved: Ce loading content = 10 wt%, calcined temperature = 200 °C. Comparing the result of the characterization and activity, it was discovered that the Pd–Ce/meso-C-200 catalyst had a large number of active surface oxygen species, Ce3+ cationic species and Pd4+ cationic species. All of these were relatively conducive to the catalytic oxidation of CO.

Influence of promoter on the catalytic activity of high performance Pd/PATP catalysts.

A series of Pd-M/PATP (M=Fe, Cu, Ce) catalysts applied in low temperature CO oxidation were prepared by a deposition-precipitation (DP) method. The techniques of N2 adsorption/desorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), temperature-programmed reduction by H2 (H2-TPR), BET and ICP were employed for catalyst characterization. It was found that the Pd-Fe/PATP catalyst had superior activity than Pd-Cu/PATP and Pd-Ce/PATP catalyst under similar condition. The characterization results showed Pd nanoparticles of Pd-Fe/PATP catalyst were dispersed highly and small size. The effects of Fe loading content, calcination temperature and H2 reduction on low temperature CO catalytic oxidation were also investigated in detail. At 10 wt.% Fe loading, the catalyst which was calcined at 200°C and no reduced with H2 had the highest activity. An additional reduction peak which was indicated by H2-TPR in the range of 200-250°C (beside Pd oxide and Fe2O3) was detected in Pd-Fe-PATP catalyst when Fe content was 10 wt.%. It was ascribed to the reduction of weakly chemical-adsorbed oxygen and was very important to enhance the activity of Pd-Fe/PATP catalysts. From the analysis of research result, it could be seen that reaction pathway for low-temperature CO oxidation over Pd-Fe/ATP was due to the Langmuir-Hinshelwood reaction mechanism.

Deposition of Pd– Fe nanoparticles onto carbon spheres with controllable diameters and applied for CO catalytic oxidation

In this paper, a series of Pd–Fe/carbon sphere (CS) catalysts were prepared by a co-precipitation method and applied in low-temperature CO oxidation reactions. The effect of the particle sizes of carbon spheres, calcination temperatures of catalysts, Pd loadings and H2 reduction were investigated in detail. SEM and TEM characterizations of carbon spheres that were prepared by a hydrothermal method indicated non-porous structure, and the CSs surface was covered by Pd–Fe composites after the preparation of the catalyst. The XPS characterization of the catalysts showed that there were rich active oxygen species, more FeO(OH) species and more tetravalent Pd (PdO2) species on the surface of the Pd–Fe/CSs catalyst. These factors are expected be helpful for CO oxidation. When Pd loading was 1.0 wt%, the Pd–Fe/CSs (CSs were prepared by 1.0 mol L−1 glucose solution) catalyst, which was calcined at 200 °C without H2 reduction, had the highest activity.

A new method to construct hierarchical ZSM-5 zeolites with excellent catalytic activity

Desilicication and dealuminzation with weak alkaline solution and acid liquor is an effective way to construct hierarchically mesoporous without damaging its crystallinity and preserving its acidity in ZSM-5 zeolites. We investigated the influence of the concentration of NaAlO2, treatment time, temperature and the concentration of HCl on the crystallinity of ZSM-5 and characterized the products with XRD, SEM, XRF, BET, NH3-TPD, etc. The results showed that the appropriate concentration of NaAlO2 solutions extract selectively silicon from the framework of the zeolites while a small portion of aluminum would patch some parts of vacancies produced by the removal of silicon, then the HCl would dealuminize to maintain the SiO2/Al2O3 ratios, which preserved the crystallinity of ZSM-5 perfectly. Furthermore, the micro-reaction activity tests displayed that the obtained products had higher catalytic than the parent zeolites because of their optimized hierarchical micro-mesoporous.

One pot synthesis of a highly efficient mesoporous ceria–titanium catalyst for selective catalytic reduction of NO

Mesoporous ceria–titanium catalysts were synthesized by one pot hydrothermal method and used for selective catalytic reduction (SCR) of NO with nearly complete NO conversion over a wide operating temperature range. The outstanding activity of the ceria–titanium catalyst was attributed to the tunable particle size and the efficient control of surface areas and pore volume in the range of 260–400 °C by the modulation of the soft template content. Especially, ceria oxide (CeO2) active centers being highly dispersed and titanium oxide (TiO2) with sufficient surface areas and uniform pore canals are the main reasons for the excellent SCR performance. For a series of catalysts, H-Ce0.2TiOx-2 exhibited nearly complete NO conversion (99%) in the range of 260 °C to 400 °C, with excellent stability and desired resistance to H2O. In addition, we discussed the reaction and deactivation mechanisms of ceria–titanium catalysts for the SCR, resulting from better redox ability and abundant acid sites. In view of the simple process and outstanding stability of mesoporous ceria–titanium catalysts, this could be treated as an ideal candidate for real applications.

Construction of Cu–Ce/graphene catalysts via a one-step hydrothermal method and their excellent CO catalytic oxidation performance

Cu–Ce/graphene catalysts show high dispersion of metal particles and excellent activity and stability for catalytic oxidation. In this study, a hydrothermal method was used to synthesize a series of bimetallic Cu–Ce/graphene catalysts, and the effects of the proportions of Cu and Ce on CO oxidation were investigated in detail. Indispensable characterizations such as XPS, XRD, TEM, BET, and H2-TPR were conducted to explore the effect of the Cu/Ce molar ratio and the metal valence on the activity and determine the structure–performance relationship. The results showed that bimetallic supported catalysts, such as 3Cu5Ce/graphene, 1Cu1Ce/graphene, and 5Cu3Ce/graphene, possessed significant catalytic activity. Especially, the 5Cu3Ce/graphene catalyst showed highest catalytic activity for CO oxidation, the T100 value was 132 °C, and the apparent activation energy was 68.03 kJ mol−1. Furthermore, the stability of the 5Cu3Ce/graphene catalyst was outstanding, which could be maintained for at least 12 h. Moreover, the CeO2 particles were well crystalline with the size 5–9 nm in these catalysts, and the CuO nanoparticles were well dispersed on CeO2 and graphene. Notably, the ratio of Cu/Ce in the catalyst was higher, the interaction between the Ce species and the graphene was stronger, and the Cu species were more easily reduced; this was beneficial for the oxidation of CO.

Promotion effect of oxygen-containing functional groups and Fe species on Pd@graphene for CO catalytic oxidation

In this paper, a Pd/reduced graphene oxide (Pd/RGO) catalyst was successfully synthesized by a chemical reduction method with hydrazine hydrate as a reducing agent. By controlling the amount of reducing agent, the Pd/RGO catalyst showed different surface Pd loadings and graphene interlayer spacings. The Pd/Fe@RGO catalyst was prepared by Pd supported on the Fe@RGO composite which was synthesized by a hydrothermal method. In the Pd/Fe@RGO catalyst, Pd0 species and Fe3+ species were the main active components. The addition of Fe species increased the interlayer spacing of graphene, the surface loading of Pd and the content of surface active oxygen. Thus, the Pd/Fe@RGO catalyst showed the highest catalytic activity for CO oxidation, and the T100 value was 90 °C and the apparent activation energy was 86.37 kJ mol−1. The superior catalyst at 50% conversion was stable for 510 min, and under moisture the catalyst was stable for only 300 min.

Recent Progress on Establishing Structure–Activity Relationship of Catalysts for Selective Catalytic Reduction (SCR) of NO x with NH 3

Catalytic elimination is an important technique to reduce the emission of atmospheric molecular contaminants (such as NOx) efficiently. Selective catalytic reduction (SCR) is one of the most important nitrogen oxide (NOx) control technologies in the world, and catalyst plays a greatly important role in SCR process. In this field, the novel catalysts and preparation methods have attracted more and more attention in recent years due to their excellent catalytic performance. It is well accepted that catalytic performance is significantly dependent on the supports, active sites, and interaction of support and active component of the catalysts. In this paper, we present a brief review on the preparation methods of different kinds of SCR catalysts in recent years and propose some perspectives for further development. Based on the report of published literatures, the structure–activity relationship between support and active sites is deeply analyzed. Meanwhile, we review the possible catalytic mechanism, and further clarify the nature of the catalytic reactions.