Xiuzhong Fang

Methane Dry Reforming over Coke‐Resistant Mesoporous Ni‐Al2O3 Catalysts Prepared by Evaporation‐Induced Self‐Assembly Method

Mesoporous Ni‐Al2O3 catalysts were prepared in one pot following an evaporation‐induced self‐assembly method (EISA) and used for methane dry reforming. Compared with a traditional Ni/Al2O3 catalyst prepared through impregnation method (IMP), the EISA catalysts display significantly improved coke resistance and activity. It is revealed by small‐angle XRD (SXRD), N2 adsorption–desorption, and TEM that an ordered mesoporous structure was formed in the EISA catalysts, which impedes the aggregation of the Ni sites and aids in the mass transfer of the reaction. In addition, the Ni species in the reduced EISA samples more dispersed, more uniformly distributed, and have smaller crystallite size, as evidenced by XRD, H2 adsorption–desorption, and TEM results. It is speculated that these are the major reasons accounting for the significantly improved dry reforming performance of the EISA catalysts.

SnO2 nano-sheet as an efficient catalyst for CO oxidation

Abstract Polycrystalline SnO2 fine powder consisting of nano-particles (SnO2-NP), SnO2 nano-sheets (SnO2-NS), and SnO2 containing both nano-rods and nano-particles (SnO2-NR+NP) were prepared and used for CO oxidation. SnO2-NS possesses a mesoporous structure and has a higher surface area, larger pore volume, and more active species than SnO2-NP, and shows improved activity. In contrast, although SnO2-NR+NP has only a slightly higher surface area and pore volume, and slightly more active surface oxygen species than SnO2-NP, it has more exposed active (110) facets, which is the reason for its improved oxidation activity. Water vapor has only a reversible and weak influence on SnO2-NS, therefore it is a potential catalyst for emission control processes.

SnO2Promoted by Praseodymia: Novel Catalysts for CO Oxidation

Abstract Praseodymia-doped SnO2 catalysts were prepared with precipitation-deposition method and used for CO oxidation. The samples were characterized by means of Inductive Coupled Plasma Emission Spectrometery (ICP), N2 Adsortion-desorption with Brunauer–Emmett–Teller Technique (N2-BET), X-ray Podwer Diffraction (XRD), H2 Temperature Programmed Reduction (H2-TPR), Thermal Gravity Analysis–Differential Scanning Carorimetry (TGA-DSC) and X-ray Photoelectron Spectroscopy Analysis (XPS). Praseodymia was found to disperse finely onto the surface of rutile SnO2, and had some strong interaction with it, thus stabilizing the surface area of the resulted catalysts as well as producing larger amount of active oxygen species. As a consequence, the CO oxidation activity of the Sn–Pr composite metal oxide catalysts was significantly enhanced. The activity of the catalysts also improves with the increasing of praseodymia addition amount, mainly due to the formation of more active oxygen species and increased surface areas.

Ni/Ln2Zr2O7 (Ln = La, Pr, Sm and Y) catalysts for methane steam reforming: the effects of A site replacement

A series of Ln2Zr2O7 supports (Ln = La, Pr, Sm and Y) with different “A” sites were prepared by a glycine–nitrate combustion method and used to support Ni to prepare catalysts for methane steam reforming for hydrogen production. It is revealed by XRD and Raman techniques that with the decrease of the rA/rB ratio in the sequence La, Pr, Sm and Y, the structures of the compounds become less ordered with the transformation of the bulk phase from ordered pyrochlore (La2Zr2O7) to less ordered pyrochlore (Pr2Zr2O7 and Sm2Zr2O7) and subsequently to defective fluorite (Y2Zr2O7). XPS demonstrated that the oxygen vacancies and mobility of the compounds also improve with the sequence. As supports for Ni, those possessing more mobile oxygen species display evidently enhanced coke resistance. In addition, as evidenced by H2-TPR, the supported Ni active sites have a stronger interaction with those supports having a higher degree of disorder, which improves both the Ni dispersion and the thermal stability of the prepared Ni/Ln2Zr2O7. Y2Zr2O7 support with a defective fluorite structure has the highest amount of mobile oxygen species. Therefore, the Ni active species has a stronger interaction with it than with the other three supports, which results in the smallest Ni grains with the highest metallic active surface area. As a consequence, Ni/Y2Zr2O7 exhibits the highest activity, stability and coke resistance among all of the catalysts. It is concluded that A site replacement by rare earth cations with different radii influences the structures of Ln2Zr2O7 significantly, which ultimately affects the reaction performance of the prepared Ni/Ln2Zr2O7 catalysts for methane steam reforming.

SnO 2 -based solid solutions for CH 4 deep oxidation: Quantifying the lattice capacity of SnO 2 using an X-ray diffraction extrapolation method

A series of SnO 2 -based catalysts modified by Mn, Zr, Ti and Pb oxides with a Sn/M (M = Mn, Zr, Ti and Pb) molar ratio of 9/1 were prepared by a co-precipitation method and used for CH 4 and CO oxidation. The Mn 3+ , Zr 4+ , Ti 4+ and Pb 4+ cations are incorporated into the lattice of tetragonal rutile SnO 2 to form a solid solution structure. As a consequence, the surface area and thermal stability of the catalysts are improved. Moreover, the oxygen species of the modified catalysts become easier to be reduced. Therefore, the oxidation activity over the catalysts was improved, except for the one modified by Pb oxide. Manganese oxide demonstrates the best promotional effects for SnO 2 . Using an X-ray diffraction extrapolation method, the lattice capacity of SnO 2 for Mn 2 O 3 was 0.135 g Mn 2 O 3 /g SnO 2 , which indicates that to form stable solid solution, only 21% Sn 4+ cations in the lattice can be maximally replaced by Mn 3+ . If the amount of Mn 3+ cations is over the capacity, Mn 2 O 3 will be formed, which is not favorable for the activity of the catalysts. The Sn rich samples with only Sn-Mn solid solution phase show higher activity than the ones with excess Mn 2 O 3 species.

Ni Supported on LaFeO3 Perovskites for Methane Steam Reforming: On the Promotional Effects of Plasma Treatment in H2–Ar Atmosphere

Steam reforming of methane for hydrogen production was performed over Ni catalysts supported on LaFeO3 perovskites synthesized with different methods and treated by non-thermal dielectric barrier discharge plasma (DBD) in H2/Ar atmosphere. It is found that catalysts prepared by glycine–nitrate combustion and sol–gel method show better performance than the one prepared with precipitation method. With plasma treatment before calcination, the catalytic performance of all the catalysts has been evidently improved. It is revealed that plasma treating can enhance the interaction between Ni and the LaFeO3 supports, thus resulting in catalysts with improved Ni dispersion, higher thermal stability and improved surface areas. SEM and TGA-DSC results testified that on the plasma treated catalysts, carbon deposition can be suppressed. These are believed to be the major reasons accounting for the improved catalytic performance of the catalysts by plasma treatment.Graphical Abstract

Synthesis of Highly Active and Stable Ni@Al2O3 Embedded Catalyst for Methane Dry Reforming: On the Confinement Effects of Al2O3 Shells for Ni Nanoparticles

A 12 % Ni@Al2O3 catalyst was synthesized by using an inverse microemulsion technique and evaluated for the dry reforming of methane (DRM). We used TEM to reveal that the core–shell structure was formed successfully in the 12 % Ni@Al2O3 catalyst, in which the Ni nanoparticle cores with an average grain size around 10 nm are encapsulated by mesoporous Al2O3 shells. In comparison with a 12 % Ni/Al2O3 catalyst prepared by an impregnation method, much smaller Ni grain sizes and higher metallic Ni active surface areas can be achieved in the core–shell catalyst, which was evidenced by using TEM and H2 adsorption–desorption analysis. In addition, a larger amount of active oxygen species was formed on the surface of 12 % Ni@Al2O3 than on 12 % Ni/Al2O3. Importantly, the formation of the core–shell structure in 12 % Ni@Al2O3 can effectively impede the migration of the Ni active species at elevated temperatures, which prevents agglomeration. Consequently, the 12 % Ni@Al2O3 core–shell catalyst shows a remarkable activity and stability and a potent coke resistance during a 50 h durability evaluation at 800 °C for DRM. It is believed that the core–shell structure is the major factor that accounts for the superior DRM performance over that of the 12 % Ni@Al2O3 catalyst, which might open a new way for the design and development of improved catalysts for DRM for hydrogen production.

Mesoporous High-Surface-Area Copper-Tin Mixed-Oxide Nanorods: Remarkable for Carbon Monoxide Oxidation

Mesoporous, high‐surface‐area Cu–Sn mixed‐oxide nanorods were fabricated for the first time by nanocasting with the use of mesoporous KIT‐6 silica as the hard template. The Cu–Sn nanorods are significantly more active than 1 % Pd/SnO2 for the oxidation of CO and possesses long‐term durability and potent water resistance; they thus have the potential to replace noble metal catalysts for emission‐control processes.

Modifying the Surface of γ-Al2 O3 with Y2 Sn2 O7 Pyrochlore: Monolayer Dispersion Behaviour of Composite Oxides

To investigate the dispersion behaviour of composite oxides on supports, and to obtain better supports for Pd for CO oxidation, a series of Y2 Sn2 O7 /Al2 O3 composite oxides with different Y2 Sn2 O7 loadings were prepared by a deposition-precipitation method. XRD and X-ray photoelectron spectroscopic extrapolation methods revealed that, similar to single-component metal oxides, composite oxides can also disperse spontaneously on support surfaces to form a monolayer with a certain capacity. The monolayer dispersion capacity/threshold for Y2 Sn2 O7 on the surface of γ-Al2 O3 is 0.109 mmol per 100 m2 γ-Al2 O3 , corresponding to 7.2 wt % Y2 Sn2 O7 loading. This is the first work to demonstrate monolayer dispersion of a composite oxide on a support. After combining Y2 Sn2 O7 with γ-Al2 O3 , active oxygen species can be introduced onto the catalyst surfaces. Thus, the interaction between Pd and the support is strengthened, the dispersion of Pd is improved in comparison with the single-component Y2 Sn2 O7 support, and a synergistic effect is induced between Pd and the composite support, which is beneficial to catalyst activity. By tuning the γ-Al2 O3 surface with different amounts of pyrochlore Y2 Sn2 O7 , CO oxidation activity on 1 % Pd/Y2 Sn2 O7 /Al2 O3 was improved. These findings may provide new insights into the design and preparation of effective supported noble metal catalysts with lower contents of noble metals.