Yun-xiang Pan

Progresses in the Preparation of Coke Resistant Ni‐based Catalyst for Steam and CO2 Reforming of Methane

Steam reforming of methane is an extremely important process for the hydrogen and syngas production. Nickel‐based catalysts have been extensively employed in the industrial process of steam reforming because of their high activity, low cost, and the plentiful supply of Nickel. Nickel‐based catalysts have also shown high activity for CO2 reforming of methane, which has been considered as a good option, with consumption of a significant amount of carbon dioxide. However, a major challenge is that Ni catalysts have a high thermodynamic potential for coke formation during reforming reactions. For steam reforming, coke formation induces deactivation of the catalyst, especially if the carbon forms as carbon filaments. The filamentous carbon material has a high mechanical strength and can cause mechanical deformation of the catalyst. For CO2 reforming, coke formation over Ni catalyst is even more serious and leads to rapid deactivation of the catalyst. It is highly desired to design and synthesize a coke resistant Ni catalyst not only for reforming of methane, but also for reforming of other hydrocarbons (including biomass derived hydrocarbons). Herein we summarize the very recent progresses in the design, synthesis, and characterization of coke resistant Ni catalysts for steam and CO2 reforming of methane. The progresses in the use of promoters, in the effect of supporting materials and in the preparation methods have been discussed. The thermal stability, regeneration, and future development of coke resistant Ni catalysts for these processes are also briefly addressed.

Adsorption and protonation of CO2 on partially hydroxylated gamma-Al2O3 surfaces: a density functional theory study.

Adsorption and protonation of CO2 on the (110) and (100) surfaces of gamma-Al2O3 have been studied using density functional theory slab calculations. On the dry (110) and (100) surfaces, the O-Al bridge sites were found to be energetically favorable for CO2 adsorption. The adsorbed CO2 was bound in a bidentate configuration across the O-Al bridge sites, forming a carbonate species. The strongest binding with an adsorption energy of 0.80 eV occurs at the O3c-Al5c bridge site of the (100) surface. Dissociation of water across the O-Al bridge sites resulted in partially hydroxylated surfaces, and the dissociation is energetically favorable on both surfaces. Water dissociation on the (110) surface has a barrier of 0.42 eV, but the same process on the (100) surface has no barrier with respect to the isolated water molecule. On the partially hydroxylated gamma-Al2O3 surfaces, a bicarbonate species was formed by protonating the carbonate species with the protons from neighboring hydroxyl groups. The energy difference between the bicarbonate species and the coadsorbed bidentate carbonate species and hydroxyls is only 0.04 eV on the (110) surface, but the difference reaches 0.97 eV on the (100) surface. The activation barrier for forming the bicarbonate species on the (100) surface, 0.42 eV, is also lower than that on the (110) surface (0.53 eV).

Effects of Hydration and Oxygen Vacancy on CO2 Adsorption and Activation on β-Ga2O3(100)

The effects of hydration and oxygen vacancy on CO(2) adsorption on the beta-Ga(2)O(3)(100) surface have been studied using density functional theory slab calculations. Adsorbed CO(2) is activated on the dry perfect beta-Ga(2)O(3)(100) surface, resulting in a carbonate species. This adsorption is slightly endothermic, with an adsorption energy of 0.07 eV. Water is preferably adsorbed molecularly on the dry perfect beta-Ga(2)O(3)(100) surface with an adsorption energy of -0.56 eV, producing a hydrated perfect beta-Ga(2)O(3)(100) surface. Adsorption of CO(2) on the hydrated surface as a carbonate species is also endothermic, with an adsorption energy of 0.14 eV, indicating a slightly repulsive interaction when H(2)O and CO(2) are coadsorbed. The carbonate species on the hydrated perfect surface can be protonated by the coadsorbed H(2)O to a bicarbonate species, making the CO(2) adsorption exothermic, with an adsorption energy of -0.13 eV. The effect of defects on CO(2) adsorption and activation has been examined by creating an oxygen vacancy on the dry beta-Ga(2)O(3)(100) surface. The formation of an oxygen vacancy is endothermic, by 0.34 eV, with respect to a free O(2) molecule in the gas phase. Presence of the oxygen vacancy promoted the adsorption and activation of CO(2). In the most stable CO(2) adsorption configuration on the dry defective beta-Ga(2)O(3)(100) surface with an oxygen vacancy, one of the oxygen atoms of the adsorbed CO(2) occupies the oxygen vacancy site, and the CO(2) adsorption energy is -0.31 eV. Water favors dissociative adsorption at the oxygen vacancy site on the defective surface. This process is spontaneous, with a reaction energy of -0.62 eV. These results indicate that, when water and CO(2) are present in the adsorption system simultaneously, water will compete with CO(2) for the oxygen vacancy sites and impact CO(2) adsorption and conversion negatively.

Photocatalytic CO2 Reduction by Carbon-Coated Indium-Oxide Nanobelts

Indium-oxide (In2O3) nanobelts coated by a 5-nm-thick carbon layer provide an enhanced photocatalytic reduction of CO2 to CO and CH4, yielding CO and CH4 evolution rates of 126.6 and 27.9 μmol h-1, respectively, with water as reductant and Pt as co-catalyst. The carbon coat promotes the absorption of visible light, improves the separation of photoinduced electron-hole pairs, increases the chemisorption of CO2, makes more protons from water splitting participate in CO2 reduction, and thereby facilitates the photocatalytic reduction of CO2 to CO and CH4.

Promotion effects of Ga2O3 on CO2 adsorption and conversion over a SiO2-supported Ni catalyst

CO2 adsorbs physically onto SiO2 but is activated on Ga2O3-promoted SiO2, resulting in surface carbonate and bicarbonate species. Consequently, the Ni/SiO2–Ga2O3 catalyst showed a higher stability and coke resistance for CO2 reforming of methane than the Ni/SiO2 catalyst.

Photocatalytic CO2 reduction highly enhanced by oxygen vacancies on Pt-nanoparticle-dispersed gallium oxide

Photocatalytic CO2 reduction on metal-oxide-based catalysts is promising for solving the energy and environmental crises faced by mankind. The oxygen vacancy (Vo) on metal oxides is expected to be a key factor affecting the efficiency of photocatalytic CO2 reduction on metal-oxide-based catalysts. Yet, to date, the question of how an Vo influences photocatalytic CO2 reduction is still unanswered. Herein, we report that, on Vo-rich gallium oxide coated with Pt nanoparticles (Vo-rich Pt/Ga2O3), CO2 is photocatalytically reduced to CO, with a highly enhanced CO evolution rate (21.0 μmol·h−1) compared to those on Vo-poor Pt/Ga2O3 (3.9 μmol·h−1) and Pt/TiO2(P25) (6.7 μmol·h−1). We demonstrate that the Vo leads to improved CO2 adsorption and separation of the photoinduced charges on Pt/Ga2O3, thus enhancing the photocatalytic activity of Pt/Ga2O3. Rational fabrication of an Vo is thereby an attractive strategy for developing efficient catalysts for photocatalytic CO2 reduction.

Peptide Self-Assembled Biofilm with Unique Electron Transfer Flexibility for Highly Efficient Visible-Light-Driven Photocatalysis

Inspired by natural photosynthesis, biomaterial-based catalysts are being confirmed to be excellent for visible-light-driven photocatalysis, but are far less well explored. Herein, an ultrathin and uniform biofilm fabricated from cold-plasma-assisted peptide self-assembly was employed to support Eosin Y (EY) and Pt nanoparticles to form an EY/Pt/Film catalyst for photocatalytic water splitting to H2 and photocatalytic CO2 reduction with water to CO, under irradiation of visible light. The H2 evolution rate on EY/Pt/Film is 62.1 μmol h(-1), which is about 5 times higher than that on Pt/EY and 1.5 times higher than that on the EY/Pt/TiO2 catalyst. EY/Pt/Film exhibits an enhanced CO evolution rate (19.4 μmol h(-1)), as compared with Pt/EY (2.8 μmol h(-1)) and EY/Pt/TiO2 (6.1 μmol h(-1)). The outstanding activity of EY/Pt/Film results from the unique flexibility of the biofilm for an efficient transfer of the photoinduced electrons. The present work is helpful for designing efficient biomaterial-based catalysts for visible-light-driven photocatalysis and for imitating natural photosynthesis.

One-step fabrication of self-assembled peptide thin films with highly dispersed noble metal nanoparticles.

Fabrication of organic thin films with highly dispersed inorganic nanoparticles is a very challenging topic. In this work, a new approach that combines electron-induced molecular self-assembly with simultaneous nanoparticle formation by room temperature electron reduction was developed to prepare peptide thin films with highly dispersed noble metal nanoparticles. Argon glow discharge was employed as the resource of electrons. The peptide motif KLVFF (Aβ16-20) self-assembled into two-dimensional membranes under the influence of hydrated electrons, while the metal ions in solution can be simultaneously reduced by electrons to form nanoparticles. Our TEM imaging reveals that metal nanoparticles were well-distributed in the resulting peptide thin films. Our results also suggest that the size of metal nanoparticles can be tuned by varying the initial concentration of the metal ion. This simple approach can be viewed as a promising strategy to create hybrid thin films that integrate functional inorganics into biomolecule scaffolds.

Fabrication of palladium/graphene oxide composite by plasma reduction at room temperature

Pd nanoparticles were fabricated on graphene oxide (GO) using a deposition-precipitation method with a glow discharge plasma reduction at room temperature. Argon was employed as the plasma-generating gas. The novel plasma method selectively reduces the metal ions. The graphene oxide has no change with this plasma reduction according to the Fourier transform infrared analysis. The Pd nanoparticles on the GO were uniformly distributed with an average diameter of 1.6 nm. The functional groups on the GO not only prevent Pd nanoparticles from further aggregation but also provide a strong hydrophilic property to the Pd/GO composite, which can form stable colloidal dispersions in water.