High-Performance Catalytic Four-Channel Hollow Fibers with Highly Dispersed Nickel Nanoparticles Prepared by Atomic Layer Deposition for Dry Reforming of Methane

Highly dispersed nickel (Ni) nanoparticles (NPs) with an average particle size of 4.3 nm were uniformly deposited on the outer surface, the inner channel surface, and inside the pores of 20 cm long four-channel α-Al2O3hollow fibers (HFs) by atomic layer deposition (ALD) for dry reforming of methane (DRM). Cerium oxide (CeO2) was added to promote the catalytic performance of Ni/Al2O3-HF catalysts. Rationally designed filling methods, by tuning the reactor size and inert fillings, can reduce the catalyst bed voidage in a fixed bed reactor for better reactant gas distribution, effectively utilize the Ni reactive sites, and achieve excellent catalytic performance. It was found that the CeO2-promoted Ni/Al2O3-HF catalyst was highly active and highly stable without deactivation during an overall 400-h DRM test at 850 °C. CeO2with reversible valence states could participate in surface reactions; especially, the formation of CeAlO3provided sufficient surface Ce3+for CO2activation and enhanced the stability and reusability of the HF catalysts

Engineering Metal-Oxide Interface by Depositing ZrO2 overcoating on Ni/Al2O3 for Dry Reforming of Methane

Zirconium oxide (ZrO2) was deposited onto Ni/Al2O3 catalyst as overcoating by atomic layer deposition (ALD) for dry reforming of methane (DRM). High-temperature heating during H2-reduction could transform the ALD-prepared ZrO2 thin film to tetragonal phase and crack the encapsulating layer on Ni sites, which constructed a beneficial Ni-ZrOx interface. Interfacial surface oxygen vacancies on ZrO2 overcoating were induced by the partial reduction of ZrO2 surface during high-temperature H2 reduction, with the assistance of Ni. During DRM, the interfacial oxygen vacancies enhanced CO2 activation by dissociating CO2 and releasing active O, thereby limiting carbon formation. For DRM at 700 °C and 800 °C, Ni/Al2O3 with 5 cycles of ZrO2 ALD overcoating enhanced both activity and stability significantly. For a 100-h DRM test at 600 °C, no deactivation was observed for the Ni/Al2O3 catalyst with 10 cycles of ZrO2 ALD overcoating, as compared to 59% relative activity loss of Ni/Al2O3

Research priorities in observing and modeling urban weather and climate

In 2007, the world reached the unprecedented milestone of half of its people living in cities, and that proportion is projected to be 60% in 2030. The combined effect of global climate change and rapid urban growth, accompanied by economic and industrial development, will likely make city residents more vulnerable to a number of urban environmental problems, including extreme weather and climate conditions, sea-level rise, poor public health and air quality, atmospheric transport of accidental or intentional releases of toxic material, and limited water resources. One fundamental aspect of predicting the future risks and defining mitigation strategies is to understand the weather and regional climate affected by cities. For this reason, dozens of researchers from many disciplines and nations attended the Urban Weather and Climate Workshop.1 Twenty-five students from Chinese universities and institutes also took part. The presentations by the workshop's participants span a wide range of topics, from the interaction between the urban climate and energy consumption in climate-change environments to the impact of urban areas on storms and local circulations, and from the impact of urbanization on the hydrological cycle to air quality and weather prediction

Prototype Catalytic Membrane Reactor for Dimethyl Ether Synthesis Via Co2hydrogenation

Dimethyl ether (DME) has become attractive as a potential environmentally friendly substitute for diesel and liquefied petroleum gas (LPG) due to its similar properties to those of LPG, high cetane number, but less carbon emissions. In this work, we developed a novel prototype-scale catalytic membrane reactor to synthesize DME directly from CO2and renewable H2, which could address the environmental and fuel security issues in a cost-effective way. This membrane reactor was equipped with superior hydrophilic NaA zeolite membranes and bifunctional Cu-ZnO-ZrO2-Al2O3/HZSM-5 catalysts. The effects of the reaction temperature and gas hourly space velocity (GHSV) on the DME synthesis were investigated. Compared with the fixed bed catalytic reactor, the catalytic membrane reactor with a unique NaA membrane significantly enhanced the DME yield and CO2conversion from 8.71 and 21.4 to 22.8 and 33.7%, respectively. The highest DME production rate of 1.31 kg/day was achieved at 300 °C and a GHSV of 8400 mL/(g·h). This work demonstrates the feasibility of the catalytic membrane reactor for DME production via CO2 hydrogenation as an approach to market readiness

Prospect for VLBI Network Extension: the First Results of an Ad-hoc S2 Array Experiments

The Canadian S2 system gives a chance for Russian and some other radio telescopes in the world to be involved into international VLBI programs. Brief descriptions of previous S2 experiments and future possibilities are presented

Effects of Mixing Methods of Bifunctional Catalysts on Catalyst Stability of DME Synthesis via CO₂ Hydrogenation

The effects of three different mixing methods of CuO/ZnO/Al2O3 (CZA) and HZSM-5 bifunctional catalyst on the stability for dimethyl ether (DME) synthesis from carbon dioxide (CO2) hydrogenation were investigated. When the bifunctional catalyst was prepared by method A (mixing powder without pelletization), there was no significant change in DME production and catalyst stability when the HZSM-5 loading was varied between 0.1 g and 0.5 g with a fixed CZA loading of 0.5 g,. When the bifunctional catalysts were prepared by method B (pressed into pellets of CZA and pellets of HZSM-5 and then mixed) and method C (mixed CZA and HZSM-5 powders, then pressed into pellets), the mixing methods did not initially impact CO2 conversion and had a minor effect on DME yield. However, long-term tests (100 h) indicated that the mixing method had a significant influence on the catalyst stability. Method B showed the best stability and the extent of catalyst deactivation followed the sequence of method B \u3c method A \u3c method C. Characterizations of spent catalysts indicated that method B could reduce the extent of copper (Cu) oxidation, which due to the relatively low surface contact between Cu active sites and HZSM-5. Large amounts of water generated in CO2 hydrogenation to synthesize DME and intimate contact between CZA and HZSM-5 catalyst could induce severe oxidation of Cu and metal ions migration from hydrogenation catalyst to HZSM-5, which can result in the number reduction of acidic sites

Enhanced Activity and Stability of MgO-Promoted Ni/Al₂O₃ Catalyst for Dry Reforming of Methane: Role of MgO

Highly dispersed nickel nanoparticles (NPs) were deposited on Al2O3 NPs by atomic layer deposition (ALD). Various amounts of MgO were loaded on Ni/Al2O3 catalysts by the incipient wetness (IW) method for dry reforming of methane. Fresh and used catalysts were systematically characterized to reveal the effects of MgO on the catalytic performance. MgO was found to increase the basic amount and basic strength of catalyst surfaces, which provided additional surface oxygen species and assisted the adsorption and activation of CO2. Although the formation of NiO-MgO solid solution, during the calcination of incipient wetness, did not improve the overall reducibility, the Ni NPs from NiO-MgO solid solution after reduction formed an intimate interaction with MgO, which could inhibit Ni NPs from sintering and provide sufficient metal-support interface for CO2 activation. The MgO-promoted Ni/Al2O3 reached a methane reforming rate of 1780 LCH4gNi-1h-1 at 850 °C, which is 26% more than that of the pristine Ni/Al2O3 . The higher CO2 activity enhanced the oxidation rate of the surface carbon generated from side-reactions, thereby resulting in a higher reforming rate and inhibiting coke formation, especially the detrimental graphitic encapsulating carbon on the active nickel surface

Engineering Metal-Oxide Interface by Depositing ZrO₂ Overcoating on Ni/Al₂O₃ for Dry Reforming of Methane

Zirconium oxide (ZrO2) was deposited onto Ni/Al2O3 catalyst as overcoating by atomic layer deposition (ALD) for dry reforming of methane (DRM). High-temperature heating during H2-reduction could transform the ALD-prepared ZrO2 thin film to tetragonal phase and crack the encapsulating layer on Ni sites, which constructed a beneficial Ni-ZrOx interface. Interfacial surface oxygen vacancies on ZrO2 overcoating were induced by the partial reduction of ZrO2 surface during high-temperature H2 reduction, with the assistance of Ni. During DRM, the interfacial oxygen vacancies enhanced CO2 activation by dissociating CO2 and releasing active O, thereby limiting carbon formation. For DRM at 700 °C and 800 °C, Ni/Al2O3 with 5 cycles of ZrO2 ALD overcoating enhanced both activity and stability significantly. For a 100-h DRM test at 600 °C, no deactivation was observed for the Ni/Al2O3 catalyst with 10 cycles of ZrO2 ALD overcoating, as compared to 59% relative activity loss of Ni/Al2O3

Enhancing DMC Production from CO₂: Tuning Oxygen Vacancies and In Situ Water Removal

The direct synthesis of dimethyl carbonate (DMC) from methanol and CO2 presents an attractive route to turn abundant CO2 into value-added chemicals. However, insufficient DMC yields arise due to the inert nature of CO2 and the limitations of reaction equilibrium. Oxygen vacancies are known to facilitate CO2 activation and improve catalytic performance. In this work, we have demonstrated that tuning oxygen vacancies in catalysts and implementing in situ water removal can enable highly efficient DMC production from CO2. CexZryO2 nanorods with abundant oxygen vacancies were synthesized via a hydrothermal method. In liquid-phase DMC synthesis, the Ce10Zr1O2 nanorods exhibited a 1.7- and 1.4-times higher DMC yield compared to CeO2 nanoparticles and undoped CeO2 nanorods, respectively. Zr doping yielded a CeZr solid solution with increased oxygen vacancies, promoting CO2 adsorption and activation. In addition, adding 2-cyanopyridine as an organic dehydrating agent achieved an outstanding 87% methanol conversion and >99% DMC selectivity by shifting the reaction equilibrium to the desired product. Moreover, mixing CeO2 nanoparticles with hydrophobic fumed SiO2 in gas-phase DMC synthesis led to a doubling of DMC yield. This significant increase was attributed to the faster diffusion of water molecules away from the catalyst surface, facilitated by the hydrophobic SiO2. This study illustrates an effective dual strategy of enhancing oxygen vacancies and implementing in situ water removal to boost DMC production from CO2. The strategy can also be applied to other reactions impacted by water accumulation

Highly Active and Stable Alumina Supported Nickel Nanoparticle Catalysts for Dry Reforming of Methane

A highly stable and extremely active nickel (Ni) nanoparticle catalyst, supported on porous γ-Al2O3 particles, was prepared by atomic layer deposition (ALD). The catalyst was employed to catalyze the reaction of dry reforming of methane (DRM). The catalyst initially gave a low conversion at 850°C, but the conversion increased with an increase in reaction time, and stabilized at 93% (1730 L h-1 g Ni-1 at 850°C). After regeneration, the catalyst showed a very high methane reforming rate (1840 h-1 g Ni-1 at 850°C). The activated catalyst showed exceptionally high catalytic activity and excellent stability of DRM reaction in over 300 h at temperatures that ranged from 700°C to 850°C. The excellent stability of the catalyst resulted from the formation of NiAl2O4 spinel. The high catalytic activity was due to the high dispersion of Ni nanoparticles deposited by ALD and the reduction of NiAl2O4 spinel to Ni during the DRM reaction at 850°C. It was verified that NiAl2O4 can be reduced to Ni in a reductive gas mixture (i.e., carbon monoxide and hydrogen) during the reaction at 850°C, but not by H2 alone