Zhoufeng Bian

A Review on Bimetallic Nickel-Based Catalysts for CO2 Reforming of Methane

In recent years, CO2 reforming of methane (dry reforming of methane, DRM) has become an attractive research area because it converts two major greenhouse gasses into syngas (CO and H2 ), which can be directly used as fuel or feedstock for the chemical industry. Ni-based catalysts have been extensively used for DRM because of its low cost and good activity. A major concern with Ni-based catalysts in DRM is severe carbon deposition leading to catalyst deactivation, and a lot of effort has been put into the design and synthesis of stable Ni catalysts with high carbon resistance. One effective and practical strategy is to introduce a second metal to obtain bimetallic Ni-based catalysts. The synergistic effect between Ni and the second metal has been shown to increase the carbon resistance of the catalyst significantly. In this review, a detailed discussion on the development of bimetallic Ni-based catalysts for DRM including nickel alloyed with noble metals (Pt, Ru, Ir etc.) and transition metals (Co, Fe, Cu) is presented. Special emphasis has been provided on the underlying principles that lead to synergistic effects and enhance catalyst performance. Finally, an outlook is presented for the future development of Ni-based bimetallic catalysts.

Sandwich‐Like Silica@Ni@Silica Multicore–Shell Catalyst for the Low‐Temperature Dry Reforming of Methane: Confinement Effect Against Carbon Formation

We synthesize a new sandwich‐like silica@Ni@silica multicore–shell catalyst. Firstly, Ni phyllosilicate (NiPS) is supported on silica nanospheres by a simple ammonia evaporation method. Then NiPS is coated with a layer of mesoporous silica to obtain a core–shell NiPS@silica structure by the hydrolysis of tetraethylorthosilicate (TEOS). The thickness of the shell can be tuned by varying the amount of TEOS. After calcination and H2 reduction at high temperature, multiple small Ni nanoparticles (≈6 nm) are generated and supported on the inner silica core but also encapsulated within the outer mesoporous silica shell. This silica@Ni@silica multicore–shell catalyst shows a high and stable conversion (≈60 %, gas hourly space velocity=60 000 mL h−1 gcat−1) for the dry reforming of methane (DRM) at 600 °C, whereas pristine NiPS deactivates quickly because of heavy carbon formation. We investigated the spent catalysts by using thermogravimetric analysis and TEM and found that there is almost no carbon formation for this new multicore–shell catalyst. Compared with a conventional Ni@silica core–shell catalyst, our multicore–shell catalyst is much easier to synthesize and the process does not require any toxic organic solvents. We believe that this strategy to make a multicore–shell catalyst can be applied to more nanomaterials and extended to other catalytic reactions besides DRM.

Sulfur resistant LaxCe1−xNi0.5Cu0.5O3 catalysts for an ultra-high temperature water gas shift reaction

A series of LaxCe1−xNi0.5Cu0.5O3 catalysts was synthesized to study the effect of Ce substitution for La. XRD results show that only a small amount of Ce (10%) is allowable to substitute La to maintain the perovskite structure. The La0.9Ce0.1Ni0.5Cu0.5O3 catalyst has the smallest metal particle size and the highest oxygen mobility among all tested catalysts as observed from the XRD, TPD-O2, and XPS results of reduced catalysts. These two factors are very important in achieving the highest catalytic activity of the La0.9Ce0.1Ni0.5Cu0.5O3 catalyst in a water gas shift reaction at 450–650 °C. In the presence of H2S, the catalytic activity at lower temperature was suppressed due to the formation of stable SO42− species on the metal. However, since the amounts of surface oxygen species and adsorbed H2S are much lower at high temperature, the formation of SO42− species is not observed, resulting in higher catalytic activity. The presence of H2S at high temperature enhances the formation of formate species, which can decompose to produce methane as the side product of the water gas shift reaction.

Ni-phyllosilicate structure derived Ni–SiO2–MgO catalysts for bi-reforming applications: acidity, basicity and thermal stability

In this work, Ni–SiO2–MgO materials synthesized via Ni-phyllosilicate (PS) intermediates were explored for bi-reforming of methane (BRM) reaction. The influence of steam and reaction temperature was also investigated for the BRM reaction. Overall, the 15 wt% Ni–30 wt% SiO2–55 wt% MgO (Ni–SiO2–MgO[55]) catalyst maintained exceptional catalytic performance (CH4 and CO2 conversions were 80% and 60%, respectively) at 750 °C for 140 h with negligible carbon deposition and also showed a stable H2/CO of 2.0. The best catalytic performance of the Ni–SiO2–MgO[55] catalyst is attributed to its enhanced basicity strength, reasonable moderate acidity strength and structural stability during high temperature reforming reaction. The formation and presence of Ni–Mg-containing phyllosilicates in fresh and reduced catalysts respectively was confirmed by TEM images and XRD analysis. The Tmax of around 750 °C in TPR profiles of Ni/SiO2–MgO catalysts further confirms the strength of interactions between Ni and SiO2–MgO support species.