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We developed a rapid aging method for Ni/Al2O3 methanation catalysts mimicking the real aging in the actual application. The method is based on hydrothermal deactivation of the catalyst at 600 or 700 °C, which leads to a catalyst with nearly constant conversion after a much shorter time period compared to normal aging. The hydrothermally aged catalysts are characterized by N2 adsorption, X-ray powder diffraction, temperature-programmed reduction and H2 chemisorption. The catalytic performance of the aged catalysts is comparable to the one of a catalyst deactivated in a long-term measurement with up to 720 h on stream. The time needed for reaching a stable conversion can be diminished by rapid aging by a factor of 10. The investigations also showed that the long-term deactivation is caused by Ni particle sintering and that the support pores limit the Ni particle size. [ABSTRACT FROM AUTHOR]

Alumina oxide supported nickel (Ni/Al2O3) catalysts generally suffer from fast deactivation caused by coking and formation of nickel aluminate (NiAl2O4) in dry reforming of methane (DRM). Herein, for the first time, a self-stabilization mechanism of the Ni/Al2O3 catalyst (with 0.1 wt% Ni loading) was revealed and effectively applied for DRM. Namely, the conversion of catalytically active Ni species into catalytically inert NiAl2O4 spinel in DRM over the Ni/γ-Al2O3 catalyst could be mitigated by repeated reduction-reaction treatments owing to the increasing amount of Ni located on the NiAl2O4 isolation layer rather than the reactive γ-Al2O3. The self-stabilization could be achieved over Ni/α-Al2O3 as well, even with a faster rate, since the NiAl2O4 isolation layer can be directly formed in the first reduction-reaction cycle due to its small surface area and weak metal-support interaction. These observations not only highlight the importance of an isolation layer for protecting the catalyst from deactivation, but also provide a novel and efficient self-stabilization approach for catalytic DRM. [ABSTRACT FROM AUTHOR]

Liquid phase hydrodearomatization (HDA) of monoaromatic model molecules (toluene, indane, tetralin, cyclohexylbenzene, nonylbenzene) from naphtha and middle distillate was conducted at a temperature of 170 °C and a pressure of 100 bar over Ni/Al2O3 in order to compare their reactivity separately and in mixture. A reactivity scale was established where toluene is more reactive than tetralin, indane, cyclohexylbenzene and nonylbenzene. The difference of reactivity is due to steric hindrance of the substituent and its electronic effect. In all cases, the fully hydrogenated product is the main product. Toluene hydrodearomatization is inhibited by the presence of another monoaromatics. This inhibition effect is more significant with indane than with cyclohexylbenzene and nonylbenzene and tetralin corresponding to competitive adsorptions and highlighted by kinetic modeling.Graphical Abstract: [ABSTRACT FROM AUTHOR]

Nitrogen containing nano-structured carbon catalysts were grown on Fe/Al2O3 and Ni/Al2O3 supports using acetonitrile pyrolysis. The post-pyrolysis samples were tested for activity in the oxygen reduction reaction (ORR) and oxidative dehydrogenation (ODH) reaction. Samples were characterized using BET, XPS and TEM. The samples grown over iron containing supports gave the highest activity in both reactions. There was a strong correlation between ODH and ORR activity suggesting the possibility of a common active site between reactions with the quinone/hydroquinone group being a possible candidate. XPS analysis supported this hypothesis showing that catalysts with a higher percentage of oxygen in the form of quinones tend to have the highest ORR and ODH activity. XPS analysis also demonstrated that samples with higher pyridinic nitrogen content, which is a marker for edge plane exposure and may be a part of the ORR active site, gave higher ORR and ODH activity. TEM images confirm that samples with high pyridinic nitrogen content tend to form structures with higher edge plane exposure. Because the active site, regardless of its identity, likely lies on the graphitic edge plane, this leaves the possibility that a common active site is not necessary to explain the correlation between ODH and ORR activity. Nitrogen containing, nano-structured carbon catalysts were shown to exhibit a correlation between the activities of oxidative dehydrogenation and electrocatalytic oxygen reduction reactions.[Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Two Ni/Al2O3 catalysts with high Ni loadings of 36 wt% and 48 wt%, which possess high activities for aqueous-phase reforming of glucose, have been successfully prepared by a novel two-step impregnation method. The catalytic performance was investigated at 533 K and autogenous pressure in a batch reactor and a significant enhancement in hydrogen yield was observed over the catalyst prepared by two-step impregnation as compared to the corresponding catalyst prepared by conventional single impregnation. The catalysts were characterized by XRD, N2 adsorption/desorption, H2 chemisorption, O2 uptake, TPO, H2-TPR and TEM. It was found that two-step impregnation yielded catalysts with higher nickel dispersion as well as smaller nickel particle size compared to single impregnation. [ABSTRACT FROM AUTHOR]

CO adsorbed infrared spectroscopy study was conducted in this work in order to better understand the significantly improved anti-coke performance of Ni/Al2O3 catalyst obtained via argon glow discharge plasma treatment. The present study revealed a significant decrease of linear to bridge (L/B) adsorbed CO for glow discharge plasma treated Ni/Al2O3, compared to that for untreated Ni/Al2O3, indicating an enhancement of close packed plane concentration. This structure change leads to lower methane turnover frequency (TOF) and better balance of carbon formation-gasification, resulting in better anti-coke property of Ni/Al2O3 for CO2 reforming of methane. [ABSTRACT FROM AUTHOR]

Ni/Al2O3 catalysts were prepared by the spray reaction method. The NiO particles supported on NiAl2O4 were stabilized against the aggregation and converted into smaller Ni particles by H2 reduction. The Ni particles stabilized on NiAl2O4 marked anomalous high activity for CO hydrogenation, due to the stronger interaction between Ni and NiAl2O4. [ABSTRACT FROM AUTHOR]

The effect of gas phase O2 and reversibly adsorbed oxygen on the decomposition of CH4 and the surface state of a Ni/Al2O3 catalyst during partial oxidation of CH4 were studied using the transient response technique at atmospheric pressure and 700°C. The results show that, when the catalyst surface is completely oxidized under experimental conditions, only a small amount of CO and H2 can be produced from non selective oxidation of CH4 by reversibly adsorbed oxygen which is more active in oxidizing CH4 completely than NiO via the Rideal–Eley mechanism and both the conversions of CH4 and O2 and the selectivities to CO and H2 are very low. Therefore, keeping the catalyst surface in the reduced state is the precondition of high conversion of CH4 and high selectivities to CO and H2. The surface state of the catalyst decides the reaction mechanism and plays a very important role in the conversions and selectivities of partial oxidation of CH4. During partial oxidation of CH4, no oxygen species but a small amount of carbon exists on the catalyst surface, which is favorable for maintaining the catalyst in the reduced state and the selectivity of CO. The results also indicate that direct oxidation is the main route for partial oxidation of CH4, and the indirect oxidation mechanism is not able to gain dominance in the reaction under the experimental conditions. [ABSTRACT FROM AUTHOR]