Lanthanum-Modified MCF-Derived Nickel Phyllosilicate Catalyst for Enhanced CO₂ Methanation: A Comprehensive Study

For the traditional preparation method, it is challenging to fabricate a supported nickel catalyst with fine size at high loading. In this work, a group of La-modified mesostructured cellular foam (MCF)-derived nickel phyllosilicates was designed and synthetized by a hydrothermal method followed by an impregnation-modification of La2O3, whose Ni contents varied from 25.3 to 32.2 wt %. Both the special property of phyllosilicate and the addition of a La2O3 modifier played significant roles in achieving high Ni dispersion and excellent catalytic performance. The formed nickel phyllosilicate was beneficial to obtain small Ni nanoparticles (<5 nm) due to its strong metal–support interaction and high specific surface area; the addition of the La2O3 modifier could further reduce the Ni particle size and decrease the reduction difficulty of the fabricated samples. On the contrary, a large Ni particle size of 13.0 nm was observed on the impregnated Ni/MCF (N/M-Im) catalyst with a Ni content of 31.7 wt %. As a result, the nickel phyllosilicate catalyst showed higher catalytic activity than the impregnated one, and the La modifier could further improve the catalytic activity especially at low temperature (<400 °C). Among all catalysts, the modified phyllosilicate catalyst N/M-P-32-5L with 180 °C-32 h-hydrothermal treatment and La2O3 content of 5 wt % was the best owing to its small-sized Ni particles, high H2 and CO2 chemisorption capacity, large turnover frequency (TOF) value, and low activation energy of 69.83 kJ mol–1. In addition, the intermediates of formate and CO were detected through in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis. In a 100 h-lifetime test under harsh conditions and 600 °C-steam treatment, N/M-P-32-5L showed both high sintering resistance of Ni particles and high thermal stability without the collapse of pores as well as decrease of catalytic activity, which was attributed to the special physical and chemical properties of MCF-derived nickel phyllosilicate, strong metal–support interaction over the catalyst, and the promotion of the La2O3 modifier

Plot of CO₂ emissions per unit GDP versus urbanization rate for 2000–2012.

Plot of CO2 emissions per unit GDP versus urbanization rate for 2000–2012.</p

Experimental investigation of jet-induced resuspension of indoor deposited particles

<p>Particles deposited on indoor surfaces may be resuspended and become airborne when disturbed by intensive jets. Depending on the intended purpose, the resuspension of deposited particles may be minimized or promoted. This investigation experimentally measured the resuspension of Arizona test dusts (ATDs) after a jet impingement. The simulating pulsed jets were created by a tube using compressed nitrogen gas. The jets were released into the test section in a wind tunnel that was cleaned by high-efficiency particulate air (HEPA) filters. The particle resuspension was evaluated by the dust-removal zone shapes on particle-laden plates, total dust-removal mass, and the number of airborne particles. The effects of the jet impingement heights, surface dust loads, and particle-laden plate surface roughness on particle resuspension were examined. This study revealed that sparsely deposited dusts indoors are more difficult to resuspend by jets than are densely deposited dusts. The jet impingement to a surface whose roughness is comparable to the particle diameters may cause severer airborne particle exposure than to surfaces with extremely small or large roughness values. For a high surface dust load, there is an optimal jet impingement height that can resuspend the maximum amount of the deposited dusts.</p> <p>Copyright © 2016 American Association for Aerosol Research</p

Threshold regression estimation results.

Threshold regression estimation results.</p

Urbanization and CO₂ emissions: First-differenced GMM estimators and system GMM estimators.

Urbanization and CO2 emissions: First-differenced GMM estimators and system GMM estimators.</p

Descriptive statistics for all variables.

Descriptive statistics for all variables.</p

Data of Fig 1.

(XLSX)</p

Eggshell waste as an eco-friendly and low-cost catalyst for the synthesis of <i>α, β</i>-unsaturated compounds

Three different eggshells, chicken eggshell, duck eggshell and quail eggshell, were used as the catalysts for the Knoevenagel reaction to produce α, β-unsaturated compounds in this work. To obtain the interrelationship among the factors of compositions, structure and catalytic activity, the eggshells were systematically characterized by X-ray diffraction, X-ray fluorescence, Fourier transform infrared spectrophotometry, scanning electron microscopy, and the Hammett indicator method. Eggshells showed the hierarchical and periodic three-dimensional network morphology and calcite crystal phase with the weak alkalinity. All eggshells were active for Knoevenagel reaction, and chicken eggshell showed the highest catalytic activity among them. The reaction conditions were optimized, and the optimal reaction condition was that aromatic aldehyde could efficiently react with active component methylene compound in the presence of 0.5 g chicken eggshell waste in water-ethanol (1:1, volume ratio) at room temperature. Various aromatic aldehydes and active component methylene compounds could be converted into the desired products in high yields, suggesting the high universality of different substrates in the presence of eggshell waste catalyst. In particular, the reaction of 4-cyanobenzaldehyde with malononitrile could be accomplished in 0.7 min with a yield of 99%. Eggshell waste catalysts could be used four times without significant loss in activity, demonstrating their high recyclability and eco-friendliness for the Knoevenagel reaction.</p

Data of regression estimation.

(DTA)</p

Data of Fig 2.

(XLS)</p