Qingjie Ge

CO oxidation catalyzed by oxide-supported Au25(SR)18 nanoclusters and identification of perimeter sites as active centers.

In this work, we explore the catalytic application of atomically monodisperse, thiolate-protected Au(25)(SR)(18) (where R = CH(2)CH(2)Ph) nanoclusters supported on oxides for CO oxidation. The solution phase nanoclusters were directly deposited onto various oxide supports (including TiO(2), CeO(2), and Fe(2)O(3)), and the as-prepared catalysts were evaluated for the CO oxidation reaction in a fixed bed reactor. The supports exhibited a strong effect, and the Au(25)(SR)(18)/CeO(2) catalyst was found to be much more active than the others. Interestingly, O(2) pretreatment of the catalyst at 150 °C for 1.5 h significantly enhanced the catalytic activity. Since this pretreatment temperature is well below the thiolate desorption temperature (~200 °C), the thiolate ligands should remain on the Au(25) cluster surface, indicating that the CO oxidation reaction is catalyzed by intact Au(25)(SR)(18)/CeO(2). We further found that increasing the O(2) pretreatment temperature to 250 °C (above the thiolate desorption temperature) did not lead to any further increase in activity at all reaction temperatures from room temperature to 100 °C. These results are in striking contrast with the common thought that surface thiolates must be removed-as is often done in the literature work-before the catalyst can exert high catalytic activity. The 150 °C O(2)-pretreated Au(25)(SR)(18)/CeO(2) catalyst offers ~94% CO conversion at 80 °C and ~100% conversion at 100 °C. The effect of water vapor on the catalytic performance is also investigated. Our results imply that the perimeter sites of the interface of Au(25)(SR)(18)/CeO(2) should be the active centers. The intact structure of the Au(25)(SR)(18) catalyst in the CO oxidation process allows one to gain mechanistic insight into the catalytic reaction.

Directly converting CO 2 into a gasoline fuel

The direct production of liquid fuels from CO2 hydrogenation has attracted enormous interest for its significant roles in mitigating CO2 emissions and reducing dependence on petrochemicals. Here we report a highly efficient, stable and multifunctional Na–Fe3O4/HZSM-5 catalyst, which can directly convert CO2 to gasoline-range (C5–C11) hydrocarbons with selectivity up to 78% of all hydrocarbons while only 4% methane at a CO2 conversion of 22% under industrial relevant conditions. It is achieved by a multifunctional catalyst providing three types of active sites (Fe3O4, Fe5C2 and acid sites), which cooperatively catalyse a tandem reaction. More significantly, the appropriate proximity of three types of active sites plays a crucial role in the successive and synergetic catalytic conversion of CO2 to gasoline. The multifunctional catalyst, exhibiting a remarkable stability for 1,000 h on stream, definitely has the potential to be a promising industrial catalyst for CO2 utilization to liquid fuels.

CeO2-supported Au38(SR)24 nanocluster catalysts for CO oxidation: a comparison of ligand-on and -off catalysts

The catalytic properties of atomically precise, thiolate-protected Au38(SR)24 (R = CH2CH2Ph) nanoclusters supported on CeO2 were investigated for CO oxidation in a fixed bed quartz reactor. Oxygen (O2) thermal pretreatment of Au38(SR)24/CeO2 at a temperature between 100 and 175 °C largely enhanced the catalytic activity, while pretreatment at higher temperatures (>200 °C) for removing thiolate instead gave rise to a somewhat lower activity than that for 175 °C pretreatment, and the ligand-off clusters were also found to be less stable. The CO conversion in the case of wet feed-gas (i.e. the presence of H2O vapor) was appreciably higher than the case of dry feed-gas when the reaction temperature was kept relatively low (between 60 and 80 °C), and interestingly the ligand-on and ligand-off catalysts exhibited opposite response to water vapor. Finally, we discussed some insights into the catalytic reaction involving the well-defined gold nanocluster catalyst.

New insights into the effect of sodium on Fe3O4- based nanocatalysts for CO2 hydrogenation to light olefins

A series of Fe3O4-based nanocatalysts with different residual sodium contents were prepared by a simple one-pot synthesis method. The effects of residual sodium on the physico-chemical properties and catalytic performance for CO2 hydrogenation of the catalysts were investigated. The residual sodium has significant influences on the textural properties of the iron-based catalysts, and slightly hinders the reduction of the catalysts. However, it obviously promotes the surface basicity of the catalysts, which is favored for olefin production. Furthermore, increasing sodium content can greatly improve the carbonization of the iron catalysts. Compared with the sodium-free Fe3O4 catalysts, the sodium-containing Fe3O4 catalysts exhibited higher activity and produced more C2–C4 olefins and C5+ hydrocarbons. The optimized FeNa(1.18) (Na/Fe weight ratio of 1.18/100) catalyst showed excellent catalytic activity with a high olefin/paraffin ratio (6.2) and selectivity to C2–C4 olefins (46.6%) and C5+ (30.1%), as well as low CO and CH4 production at a CO2 conversion of 40.5%.

Influences of Precipitate Rinsing Solvents on Ni Catalyst for Methane Decomposition to COx-free Hydrogen†

Influences of precipitate rinsing solvents on Ni for methane decomposition to CO(x)-free hydrogen has been investigated in this study. Calcination of nickel hydroxide precipitates rinsed by ethanol leads to the formation of nanosheet needle-like NiO, whereas calcination of those rinsed by deionized water leads to the formation of pure nanosheet NiO. When compared to Ni catalyst (Ni-et) reduced from nanosheet needle-like NiO, Ni catalyst (Ni-etwt), reduced from pure nanosheet-like NiO, exhibits a better catalytic performance for methane decomposition. Among the different rinsing processes, nickel hydroxide precipitates, rinsed first by ethanol and subsequently by deionized water, were calcined to the most suitable nanosheet NiO, which could be reduced to Ni-etwt catalyst with the highest catalytic performance of methane decomposition. A total of 1954 mol(H2)/mol(Ni) of hydrogen yields could be obtained over Ni-etwt under suitable reaction conditions. Characterization results indicate that Ni-etwt with the higher catalytic activity has the approximately 34 nm of average particle size.

The Unique Role of CaO in Stabilizing the Pt/Al2O3 Catalyst for the Dehydrogenation of Cyclohexane

Coke‐induced deactivation is one of the major challenges in the field of heterogeneous catalysis. Herein, the performance of the Pt/Al2O3 catalyst for the hydrogen‐free dehydrogenation of cyclohexane was improved by doping with a small amount of Ca. The Ca‐modified Pt/Al2O3 catalyst exhibited a cyclohexane conversion of 97.0 % and maintained a conversion above 75 % after 48 h, whilst the unmodified catalyst was deactivated from 87.0 to 2.7 % under the same conditions. Characterization techniques, including in situ DRIFT, XPS, thermal analysis, and temperature‐programmed techniques, revealed that the presence of Ca effectively suppressed the deep dehydrogenation of H‐rich carbonaceous components and promoted coke desorption by increasing the H/C ratio of H‐deficient coke. This promotion effect of Ca was also associated with neutralizing the residual Cl ions and promoting immediate dehydrogenation.

A comparative study of PdZSM-5, Pdβ, and PdY in hybrid catalysts for syngas to hydrocarbon conversion

The catalytic conversion of syngas into hydrocarbons over hybrid catalysts consisting of a methanol synthesis catalyst and Pd modified zeolites (PdZSM-5, Pdβ, and PdY) was investigated. The results indicate that the intermediate dehydration step of DME in the syngas to hydrocarbon process mainly occurs on the Bronsted acid sites of the Pd zeolite. The large pores and cavities of Pdβ and PdY promote the formation of C4+ hydrocarbons, which are mainly gasoline-type branched hydrocarbons. Moreover, the large pores and cavities provide enough space for the formation of higher aromatics which are the precursor of coke. The blockage of micropores of the Pd zeolites by hydrocarbon-type coke results in the deactivation of the hybrid catalysts.

Comparative study of silica-supported copper catalysts prepared by different methods: formation and transition of copper phyllosilicate

Cu/SiO2 catalysts prepared by ion exchange (IE), deposition precipitation (DP), homogeneous deposition–precipitation (HDP) using urea hydrolysis and ammonia evaporation (AE) were systematically characterized focusing on the formation and transition of copper phyllosilicate. It was generated during the AE, IE and HDP methods and decomposed to CuO after calcination at 450 °C, which was supported by BET, TPR, XRD and TEM. Copper phyllosilicate can be reduced to Cu0 rather than Cu+ below 350 °C. The formation of copper phyllosilicate promoted the dispersion of copper species. The Cu/SiO2 catalyst prepared by the AE method possessed the highest Cu0 dispersion due to the high content of copper phyllosilicate in the catalyst precursor and thus exhibited the best activity for the hydrogenation of methyl acetate.

Effect of Ca promoter on LPG synthesis from syngas over hybrid catalyst

Direct synthesis of liquefied petroleum gas (LPG) from syngas was carried out over hybrid catalyst consisting of methanol synthesis catalyst and Y zeolite modified with Pd and Ca by different methods. The decrease of CO conversion was mostly attributable to the sintering of Cu in methanol synthesis catalyst. On the other hand, coke deposition on the Y zeolite was the main reason for the decrease of LPG selectivity. The introduction of Ca decreased the strong acid sites of Y zeolite, suppressed coke formation, and thus improved the stability of hybrid catalyst.

Influences of reaction conditions on methane decomposition over non-supported Ni catalyst

Abstract Effects of reaction temperature and methane gas hourly space velocity (GHSV) on methane decomposition over non-supported Ni catalyst have been investigated in this work. Methane molecules activation, Ni particles growth and nano-carbon diffusion were the main factors influencing methane decomposition stability of non-supported Ni. The results of methane decomposition activity test on the non-supported Ni catalyst showed that the prepared non-supported Ni could exhibit a good methane decomposition performance with 273 g C /g Ni and 2667 mol H2 /mol Ni at 500 °C and 45000 mL/(g cat h). Scanning electron microscope (SEM), X-ray powder diffraction (XRD) and temperature-programmed oxidation (TPO) have been carried out to characterize the used catalysts. The deposited carbon was carbon nanofibers, among which graphitic carbon formation increased with the reaction time of methane decomposition. Ni particle size was not the decisive factor during the carbon growing stage.