1,721,002 research outputs found
Tailoring the mechanochemical interaction between vanadium oxides and zeolite for sulfur-resistant DeNOx catalysts
No full text© 2022 Elsevier B.V.Utilizing mechanochemical interactions to fabricate hybrid catalysts composed of two or more materials is an important emerging area in heterogeneous catalysis. Here, we report unusual deactivation of vanadia catalyst derived from mechanical grinding with Al-rich zeolite, initially designed to overcome the ammonium bisulfate poisoning in low-temperature selective catalytic reduction (SCR) of NOx. Various characterizations reveal that mechanical force applied to zeolite imparts mobility to extra-framework AlOx moieties. Some of the diffused AlOx species bound to VOx sites lower reducibility of catalyst, degrading its initial performance. These phenomena are effectively resolved by novel strategy of covering the surface of zeolite with a thin carbon layer, suppressing the diffusion of AlOx moieties during grinding. The hybrid catalyst prepared by tailoring mechanochemical interaction demonstrates superior sulfur resistance in low-temperature (180 °C) SCR operation. Our study critically describes effects of mechanical forces on catalytic properties and efficient modulation of these interactions through surface functionalization.N
Enhancement in the metal efficiency of Ru/TiO2 catalyst for guaiacol hydrogenation via hydrogen spillover in the liquid phase
No full text© 2022 Elsevier Inc.Decrease in the metal dispersion of noble-metal-loaded catalysts with high metal loading is a major factor reducing noble-metal efficiency. Herein, we investigated the enhancement in metal efficiency of Ru/TiO2 catalyst by utilizing hydrogen spillover in the liquid-phase. Ru was highly dispersed at low loadings (0.1 and 0.5 wt%), while larger nanoparticles were formed at higher loadings (1–5 wt%). The hydrogen spillover in liquid phase was activated at reaction temperature (100 °C) as the Ru dispersion decreased, which was confirmed through physical dilution experiments, hydrogen temperature-programmed-reduction, and kinetic analysis. Isotope experiment was conducted using D2O, observing inverse kinetic isotope effect (IKIE) for the high-Ru-loading catalysts. Based on the understanding of the hydrogen spillover in the liquid phase, the low metal efficiency of high-Ru-loading catalysts resulting from low dispersion could be compensated simply by physically mixing pristine TiO2, which played a role as new active sites when liquid-phase hydrogen spillover was activated.N
Deactivation resistance effect of alkane co-feeding on methane dehydroaromatization and active GaO+ species in Ga/HZSM-5 for BTX production
No full textAn alternative feedstock is urgently required to produce valuable aromatic compounds due to the growing demand for chemicals, drastic fluctuations in crude oil supply, and especially recent oil prices. Hence, in this study, as an alternative potential production for aromatic compounds, the codehydroaromatization of natural gas (mol ratio of CH4:C2H6:C3H8 = 85:10:5) was investigated over Ga/HZSM-5 catalysts at a relatively low temperature of 650 ?. The optimal amount of Ga loading was found to be 3 wt% for the highest aromatic formation. Profound characterizations revealed that the selective formation of GaO+ (Ga3+) is crucial to obtaining more aromatics from the natural gas feed. In addition, since methane is a significantly stable chemical, formidable energy consumption is necessary to progress reactions. The effect of light hydrocarbon co-feeding (i.e., ethane and propane) on the dehydroaromatization of methane was investigated, which resulted in methane activation at low temperatures from the natural gas composition. As a result, the aromatics formation rate in the natural gas feed was 1.5 times higher compared to the alkane co-feed (ethane and propane) and was incomparable to methane sole feed. It was demonstrated that the high aromatic formation rate resulted from the suppression of coke deposition on the external surface of the zeolite, thereby prolonging the catalytic activity. Therefore, the investigation of the codehydroaromatization of natural gas and optimal Ga loading synergistically enhances the potential of the direct use of natural gas in petrochemical industries.N
In situ spectroscopic studies of the effect of water on the redox cycle of Cu ions in Cu-SSZ-13 during selective catalytic reduction of NOx
No full textThe effect of water on the NH3-assisted selective catalytic reduction of NOx (NH3-SCR) has been largely neglected, despite the inevitable presence of water vapor in real emissions produced by fuel combustion. In this work, we investigated the role of water in the behavior of active Cu2+ ions in Cu-SSZ-13 in the NH3-SCR reaction. The addition of water to the reactant feed leads to significantly increased NOx reduction over the catalyst. By combining in situ DRIFTS and XANES analyses during the NH3-SCR reaction, we found that the redox cycle of Cu ions is promoted by the presence of water.N
Acid-site control of ZSM-5 zeolites using quaternary ammonium hydroxides for shale gas dehydroaromatization
No full textThe direct non-oxidative shale gas dehydroaromatization is a promising route for BTX (benzene, toluene, and xylenes) production, offering an effective alternative to conventional crude-oil-based processes. However, it faces crucial challenges such as rapid catalytic deactivation in Mo/ZSM-5 catalysts and limited regenerability due to the formation of external hard coke, resulting from external Mo active sites. This study introduces a hydrothermal post-treatment approach that can selectively control the external Al sites in ZSM-5 zeolites using quaternary ammonium hydroxides, aimed at reducing external Mo anchoring sites. This method successfully reduced the external Al and Mo-site densities in Mo/ZSM-5 catalysts, concurrently introducing mesoporosity, eventually leading to improved catalytic stability, reduced hard coke formation, and enhanced regenerability of spent catalysts. We highlight the significance of the roles of quaternary ammonium cations in the hydrothermal post-treatment, contrasting their effects with the NaOH treatment and analogous processes conducted at lower temperatures.N
Promotive effects of Ba addition on lean NOx reduction by CO over IrRu/ Al2O3 catalyst
No full textA series of IrRu/Al2O3 based catalysts, where Ba promoter was added in differing amounts were applied for the lean reduction of NOx using CO (CO-SCR), and the promotive effects of Ba addition were thoroughly analyzed. Below 225 degrees C, IrRu/Al2O3 catalyst exhibits high de-NOx activity, but at high temperature above 250 degrees C, suffers from drastic decline of NOx conversion. Promotion of Ba enhances the catalytic activity by suppressing NO2 production in the high temperature region, which expands the operation window. Ba species is capable of trapping the NOx species, following its traditional role as a NOx storage compartment. However, when compared to the Ba/IrRu/Al2O3 catalyst, physically mixing Ba compartment with IrRu/Al2O3 catalyst did not lead to substantial promotion. Thus, participation of Ba species during the reaction is not limited to NOx storage, where it is proposed that a continuous regeneration of NOx-trapping Ba sites takes place by direct reaction with the CO reductant catalyzed by IrRu species. It is also revealed that promotion of Ba led to fundamental alterations in IrRu species, by maintaining their active metallic states under oxidizing reaction conditions and modifying their intrinsic activity towards NO bond cleavage, thereby leading to enhanced activity at elevated temperatures. The utilization of Ba/IrRu/Al2O3 catalysts in lean NOx reduction using CO as a reductant is anticipated to enable the facile reduction of NOx over a wide temperature range with high efficiency and stability, while also eliminating the need to employ conventional urea-based reductant, even under oxidizing conditions.N
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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