Metal Dispersion Research Articles

Enhanced fischer-tropsch synthesis performance on Co@SiO2 catalyst with core-shell structure

Energy is of great importance for the development of modern society, which is mostly dependent on crude oil. Due to the severe pollution caused by using crude oil and the diminishing of crude oil reserves, it is urgent to look for clean oil from alternative resource other than crude oil. Currently, Coal-to-Liquid (CTL) or Biomass-to-Liquid (BTL) technology is an important way to produce clean liquid fuels through Fischer-Tropsch Synthesis (FTS) of syngas. For FTS process, catalyst is a main factor for affecting on syngas conversion and product distribution. For traditional oxides-supported catalysts, the mutual constraint between active metal loading and dispersion at high metal loading is hard to overcome, which will hinder the synthesis of high-performance FTS catalysts. In this paper, a new type of Co@SiO2-T (CS-T) and Co@SiO2-X (CS-X) catalysts with core-shell structure were prepared by using polyvinyl pyrrolidone (PVP) as the structural stabilizer, hexadecyl trimethyl ammonium Bromide (CTAB) as the templating agent and tetraethyl orthosilicate (TEOS) as the silica source. The effects of hydrothermal temperature and pyrolysis temperature on the catalyst physical-chemical properties and FTS performance were investigated. The results showed that increasing the hydrothermal temperature favored the formation of the core-shell structure of the catalysts. With the increase of pyrolysis temperature, the catalyst particle size decreased from 0.54 μm to 0.23 μm. The FTS activities of the catalysts showed a volcano trend with hydrothermal and pyrolysis temperatures.

Polyol-Intermediated Facile Synthesis of B5-Site-Rich Ru-Based Nanocatalysts for COx-Free Hydrogen Production via Ammonia Decomposition.

Herein, a B5-site-rich Ru/MgAl2O4 nanocatalyst for the production of COx-free hydrogen from ammonia (NH3) is synthesized using the polyol method. The polyol method enables size-sensitive Ru-nanoparticle growth and controlled B5-site formation on the catalyst by tuning the carbon-chain length of the polyol solvent used, obviating the use of a separate stabilizer and enhancing electron donation from Ru (with a high surface electron density) and π-back bonding. The Ru/MgAl2O4 (BG) catalyst synthesized using butylene glycol (a long-carbon-chain solvent) contains 2.5nm Ru particles uniformly dispersed on its surface and abundant B5 sites at (0 0 2)/(0 1 1). Moreover, the Ru/MgAl2O4 (BG) catalyst exhibits lower activation energy (48.9kJmol-1) and higher H2 formation rate (565-1,236mmol gcat -1 h-1 at 350-450°C and a weight hourly space velocity of 30,000mL gcat -1 h-1) during the NH3 decomposition reaction than catalysts with a similar Ru particle size and high metal dispersion synthesized by the impregnation and deposition-precipitation methods. This high performance is possibly because the abundant electron-donating B5 sites on the catalyst surface accelerate the recombination-desorption of N2, which is the rate-determining step of the NH3 decomposition reaction at low temperatures. Thus, this study facilitates clean hydrogen production.

Effect of composition of multicomponent supports on properties of supported Nickel catalysts

Ni catalysts supported on combinations of alumina, magnesia, zirconia with rare earth supports are studied for the steam reforming of ethanol (ESR). The composition of the supports is systematically varied to identify the role of individual components and their contribution when they are combined. Supports containing magnesia or zirconia show contrasting behavior of acidity, XRD crystallite size of NiO, reducibility, dispersion of Ni(0), OSC, coking and metals sintering characteristics. Catalyst activity and deactivation are strongly influenced due to these differences. HRTEM indicates the redispersion of Ni(0) during reduction of NiO on catalysts containing magnesia. Magnesia and alumina-magnesia based catalysts show hindered reduction of nickel and highest intrinsic activity (H2 yields). But sintering of Ni is their nemesis. Moderate interaction of Ni with zirconia-based supports (H2-TPR) lends sintering stability in ESR. Quaternary Alumina-Magnesia-Zirconia catalysts imbibe advantages of individual components and are overall best with fair H2 yield, good stability and regenerability. Long duration (80 hours) performance tests give holistic results because they encompass multiple factors influencing deactivation. Intrinsic chemical reactivity (as opposed to) active metal dispersion is important while comparing the activity of catalysts with different compositions. Degree of reducibility of nickel is an important consideration while measuring metal dispersion by chemisorption. Metal reducibility by H2-TPR, dispersion measurement by chemisorption and particle size determination by HRTEM are used as complementary techniques for rationalizing results of metal dispersion measurement.

Salt template-assisted polymer tethering strategy to achieve high dispersed cobalt single atoms/clusters on porous carbon catalysts for effective Fenton-like reactions

The exploration of the synthesis of porous carbon-supported metal nanocatalysts with high metal loading and dispersion for the development of heterogenous catalysts is important. However, this remains a challenging subject. In this paper, a salt template-assisted polymer tethering strategy was proposed to prepare Co single atom and ultrafine cluster anchored on porous carbon (Co-NPC) with a high-loading of 16.9wt%, thereby exposing high density of reaction sites. The obtained Co-NPC catalyst exhibited excellent catalytic performance for almost 100% degradation of bisphenol A (BPA) within 20min, which is much faster than the CoSA-NPC catalyst with only single atom sites and Co-NC without salt template added. Radical quenching experiments and electron paramagnetic resonance tests verified that both the nonradical oxidation pathway by 1O2, the electron transfer and radical oxidation pathway by •OH, SO4•- appeared during the degradation process. After 3 cycles, the removal rate of BPA did not decrease significantly. The fixed bed experiment revealed that Co-NPC could realize the continuous degradation of methylene blue (MB) with almost 100% degradation efficiency. This research indicated that the strategy by pyrolyzing metal coordinated polymer is a potential method for the synthesis of high metal loading catalyst at gram scale, meeting the requirement of practical applications.

Fe-promoted Ni nanocatalysts for hydrogenolysis of Klason lignin to monophenols

The efficient cleavage of lignin's inter-unit bonds is essential for its conversion into valuable monophenols. However, conventional Ni-based catalysts often suffer from poor metal dispersion, sintering, and limited catalytic activity. In this study, a series of bimetallic Ni2M/Al2O3 (M=Fe/In/Mn/Cu/Co) catalysts were synthesized using layered double hydroxides as precursors. Among the metal promoters tested, Fe showed the highest efficacy in improving catalytic performance. NixFey/Al2O3 catalysts with varying Ni/Fe molar ratios exhibited superior activity due to the formation of Ni-Fe alloys and defect-rich FeOx species. The optimized Ni1.5Fe1.5/Al2O3 catalyst, characterized by well-dispersed small metal particles, strong Ni-Fe interactions, abundant surface oxygen vacancies, and a high density of strong acid sites, achieved a monophenol yield of 16.6 wt% from the hydrogenolysis of Klason lignin under mild reaction conditions (240°C, 4 hours, 1 MPa initial H2). This work presents a novel approach for developing highly active bimetallic catalysts for lignin depolymerization, offering insights into the design of efficient catalysts for lignin valorization.

Hydrotalcite-derived well-dispersed and thermally stable cobalt nanoparticle catalyst for ammonia decomposition

Ammonia is a carbon-free hydrogen carrier, and development of non-noble metal catalyst to decompose ammonia into hydrogen is desirable for practical applications. However, the metal catalyst is challenged by the sintering of metal particles under high-temperature reaction conditions. In this study, a series of Li-, Al-, and Co-containing hydrotalcite-like compounds (HTlc) were synthesized by co-precipitation and used as precursors to prepare well-dispersed and thermally stable Co nanoparticle catalysts for ammonia decomposition. The obtained precursors and catalysts were characterized by means of X-ray powder diffraction (XRD), temperature-programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), and so on. All of the precursors formed hydrotalcite-like phase, which consisted of Li–Al–(Co) HTlc and/or Co–Al HTlc dependent on the Co content. Upon calcination at 500 °C, HTlc decomposed into an Al-substituted Co3O4 spinel oxide, as confirmed by two distinctly separated reduction steps in H2-TPR. Following reduction at 700 °C, well-dispersed Co metal nanoparticles with an average particle size of ∼9.2–12.4 nm were obtained. It was suggested that the incorporation of Al3+ into Co3O4 led to a strong interaction between cobalt and aluminum, which suppressed the crystal growth of Co3O4 and the sintering of Co metal during the thermal treatments, resulting in good Co dispersion. The optimal LiAlCo(1.5) catalyst showed superior activity than that prepared by impregnation method, giving almost complete conversion of ammonia at 575 °C under a space velocity of 5,000 mL gcat–1 h–1. More importantly, this catalyst maintained stable activity at 625 °C for 100 h, exhibiting high stability and sintering resistance. The good catalytic performance was attributed to the high Co metal dispersion and strong metal–support interaction benefiting from the uniform distribution of cobalt in the HTlc precursor. These results demonstrate the applicability of HTlc to the preparation of metal catalysts with improved dispersion and thermal stability.

Confinement and synergy effect of bimetallic Cu-Ni clusters encapsulated in Beta zeolite for methyl acetate formation from methanol alone

The direct synthesis of methyl acetate (MA) from methanol is an appealing and green approach, but an efficient catalyst is urgently needed. Herein, Cu-Ni bimetallic clusters, with a diameter of ∼1.2 nm, have been successfully encapsulated within BEA zeolite by an in-situ two-step encapsulation method (Cu-Ni@Beta), which significantly favors the dispersion of metals compared to the ion-exchanging (Cu/Ni@Beta) and wet impregnation approach (Cu-Ni/Beta). The as-synthesized Cu-Ni@Beta catalyst shows a MA formation rate of 1.46 mmol s−1 g(Cu+Ni)−1, which is much higher than Cu/Ni@Beta of 0.02 mmol s−1 g(Cu+Ni)−1 and Cu-Ni/Beta of 0.12 mmol s−1 g(Cu+Ni)−1. Characterization studies reveal that zeolite constraints could not only provide the spatial confinement for metal clusters but also induce an electronic interaction between confined Cu and Ni species in Cu-Ni@Beta. This interaction can increase and stabilize Cu+ sites as well as Lewis acid sites, which are crucial for improving catalytic performance. In-situ FTIR experiments indicate that the formation of formaldehyde (CH2O*) is the critical step for methanol to MA, and the CH2O* further couples with methoxy (CH3O*) to form acetate species (CH3CHO*), which subsequently couples with CH3O* to produce MA.

Eridanus III and DELVE 1: Carbon-rich Primordial Star Clusters or the Smallest Dwarf Galaxies?* *This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

We present spectroscopy of the ultra-faint Milky Way satellites Eridanus III (Eri III) and DELVE 1. We identify eight member stars in each satellite and place nonconstraining upper limits on their velocity and metallicity dispersions. The brightest star in each object is very metal poor, at [Fe/H] = −3.1 for Eri III and [Fe/H] = −2.8 for DELVE 1. Both of these stars exhibit large overabundances of carbon and very low abundances of the neutron-capture elements Ba and Sr, and we classify them as CEMP-no stars. Because their metallicities are well below those of the Milky Way globular cluster population, and because no CEMP-no stars have been identified in globular clusters, these chemical abundances could suggest that Eri III and DELVE 1 are dwarf galaxies. On the other hand, the two systems have half-light radii of 8 pc and 6 pc, respectively, which are more compact than any known ultra-faint dwarfs. We conclude that Eri III and DELVE 1 are either the smallest dwarf galaxies yet discovered, or they are representatives of a new class of star clusters that underwent chemical evolution distinct from that of ordinary globular clusters. In the latter scenario, such objects are likely the most primordial star clusters surviving today. These possibilities can be distinguished by future measurements of carbon and/or iron abundances for larger samples of stars or improved stellar kinematics for the two systems.

A Bifunctional Iron-Nickel Oxygen Reduction/Oxygen Evolution Catalyst for High-Performance Rechargeable Zinc-Air Batteries.

Efficient and robust electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are crucial for fuel cells, metal-air batteries, and other energy technologies. Here, a highly stable, efficient bifunctional OER/ORR electrocatalyst (FeNi-NC@MWCNTs) is reported and demonstrated its integration and robust performance in an aqueous Zinc-air battery (ZAB). The catalyst is based on neighboring iron/nickel sites (FeNiN6) which are atomically dispersed on porous nitrogen-doped carbon particles. The particles are wrapped in electrically conductive multi-walled carbon nanotubes for enhanced electrical conductivity. Electrocatalytic analyses show high OER and ORR performance (OER/ORR voltage difference = 0.69V). Catalyst integration in a ZAB results in excellent performance metrics, including an open circuit voltage of 1.44V, a specific capacity of 782 mAh g-1 (at j = 15mA cm-2), a peak power density of 218mW cm-2 (at j = 260mA cm-2) and long-term durability over 600 charge/discharge cycles. Combined experimental and theoretical (density functional theory) analyses provide an in-depth understanding of the physical and electronic structure of the catalyst and the role of the FeNi dual atom reaction site. The study therefore provides critical insights into the structure and reactivity of high-performance bifunctional OER/ORR catalysts based on atomically dispersed non-critical metals.

Metal-Organic Framework-Templated Synthesis of Nickel-Alumina Nanocatalysts Improves Catalyst-Support Interaction for Higher Activity and Stability in Biogas Reforming under Controlled Oxidizing Conditions.

Tri-reforming methane with CO2, O2, and H2O mixtures requires a delicate balance of dry-reforming, partial oxidation, and steam-reforming reactions to improve the CO2 conversion and H2/CO ratio. Nickel-alumina has been reported before for the tri-reforming of methane, although at higher temperatures (>900 °C). This is because the current approaches for nickel-alumina synthesis are ineffective in generating stronger catalyst-support interactions necessary to maintain higher active sites and stall carbon nanotube (CNT) deposition. Here, we report a synthesis method that allows controlled loading of nickel on alumina-based MIL-53 metal-organic framework followed by calcination to generate 2.5-10 wt % nickel nanoparticles dispersed on alumina. The 5 wt % nickel-alumina mixtures resulted in nanometer-sized crystallites, better metal dispersion, and more active sites for enhanced catalytic activity. This optimal loading of nickel allows stronger interaction with alumina for over 100 h of stable performance of tri-reforming at 800 °C, achieving ∼98% CH4 conversion, ∼36% CO2 conversion, and no carbon deposition while producing Fischer-Tropsch-ready feed containing a H2/CO ratio of 3.2.

Transition metal ions-chelated COFs derived bifunctional oxygen catalysts for rechargeable Zn-air batteries

Improving energy conversion efficiency and battery cycle stability is an essential goal in energy conversion and storage, while a critical factor in achieving this goal is the design of effective bifunctional catalysts. The covalent organic framework is a new type of high molecular material that can be employed as an ideal template for quantitative chelate metal ions to synthesize highly efficient bifunctional catalysts with high dispersion metal active sites. In this work, the Fe2Ni1/NiFe2O4@NCG bifunctional catalysts are constructed by employing metal-chelated COFs and MA/GO mixture as primary precursors combined with a high-temperature pyrolysis strategy. COFs and MA serve as chelators and spacers to improve the dispersion of metal nanoparticles. The Fe2Ni1/NiFe2O4@NCG composite exhibits a large BET surface area and hierarchical structure with plentiful nanoparticles on the carbon layers. HRTEM proves the coexistence of FeNi and NiFe2O4. The optimal Fe2Ni1/NiFe2O4@NCG-800 composite shows satisfactory catalytic O2 performance, providing a half-wave potential of 0.857 V for ORR and an overpotential of 244 mV for OER. Meanwhile, DFT calculations prove that electron redistribution occurs at the interface between FeNi and NiFe2O4 after combination. The Fe2Ni1/NiFe2O4@NCG-based liquid and solid-state ZABs perform very well, exhibiting large specific capacities (796 mAh·g−1 for aqueous ZAB; 742 mAh·g−1 for solid-state ZAB) and stable charge-discharge cycle performance (300 h for aqueous ZAB; 180 h for solid-state ZAB).

Highly stable Co@BC catalysts encapsulated in biochar for efficient lignin hydrogenolysis to valuable monophenols

The development and utilization of renewable lignin from industrial crops to produce high-value bio-based chemicals and fuels is of great significance in reducing dependence on fossil resources and promoting green chemistry. However, conventional metal-supported catalysts often suffer from poor metal dispersion and particle agglomeration during lignin conversion, resulting in insufficient catalytic activity. To address these challenges, a novel biochar-encapsulated cobalt catalyst (Co@BC) was developed in this study for efficient lignin hydrogenolysis. The catalyst formed a unique thin carbon layer structure by encapsulating cobalt nanoparticles in biochar, which enhanced metal dispersion and prevented particle agglomeration. The performance of the catalysts was systematically evaluated at different calcination temperatures. Co@BC-650 showed the best results with a lignin liquefaction degree of 79.7 % and a monophenol yield of 19.1 wt%. This yield was significantly higher than that of the supported Co/BC-650 catalyst, which only reached 15.4 wt%. The thin carbon layer not only facilitated the reduction of cobalt species at 650 °C, but also provided antioxidant protection and maintained the stability of metallic cobalt, which was essential for H2 adsorption and activation. In addition, Co@BC-650 exhibited excellent stability with little loss of activity after 3 cycles. This study provides an efficient and sustainable method for the selective production of monophenols from renewable lignin from industrial crops, which has the potential to be widely applied for biomass conversion and large-scale sustainable chemical production.

Efficient Hydrodeoxygenation of Lignin-Derived Phenolic Compounds Over Ru-Based Catalyst with Biochar and Al2O3 as Composite Support.

Hydrodeoxygenation (HDO) is a common strategy for upgrading lignin-derived phenolic compounds into high-quality liquid fuels, and the support rational design of HDO catalysts is critical to achieve a good reaction performance. This work proposed a novel Ru-based catalyst with biochar and Al2O3 as composite support. The addition of biochar can enlarge the porous structure, and the addition of Al2O3 can enhance the acid property of the support. By regulating the content of biochar and Al2O3 components, Ru/CA-2 catalyst achieved the best HDO performance of lignin-derived phenolic compounds, with the optimal component balance of 50 %C and 50 %Al2O3. This catalyst possesses the high Ru metal dispersion (1.38 nm particle size) to activate the hydrogen source, the moderate acid property to suppress carbon deposition and the abundant oxygen vacancy to promote substrate adsorption at the same time. 99.9 % conversion of guaiacol is obtained at 230 °C, with 99.9 % selectivity towards cyclohexane. Ru/CA-2 catalyst also has a good recyclability, with no obvious activity loss after five runs. Furthermore, in the application of catalytic lignin-oil HDO, the content of hydrocarbons increase from 10.7 % to 95.7 %, showing great potential on the industrial usage.

Cerium-induced modification of acid-base sites in Ni-zeolite catalysts for improved dry reforming of methane

Dry reforming of methane (DRM) is a promising route to mitigate greenhouse gas emissions by converting CH4 and CO2 into valuable syngas. The present work explores the effect of Ce addition to Ni-based catalysts supported on CBV3020E (ZSM-5) for DRM. The use of Ce as a promoter to tune the acid-base properties of zeolites for DRM is addressed for the first time in detail. While Ce has traditionally been used to improve oxygen storage capacity, this work explores its novel use as a means to enhance surface basicity and promote CO2 adsorption. The samples were prepared by wet impregnation, characterized using N2-sorption, X-ray diffraction, H2-temperature-programmed reduction, temperature-programmed desorption of CO2 and ammonia, and Fourier transforms infrared spectroscopy, and tested for DRM at 800 °C and 42,000 mL/g.h GHSV. Results show that ZSM-5 zeolite can be beneficial in achieving high metal dispersion. The introduction of 2 wt% Ce to Ni5/ZSM-5 increases the concentration of strong basic sites, resulting in improved catalytic performance from 37 % CH4 conversion and 48 % CO2 conversion for Ni5/ZSM-5 to 55 % and 65 % on promoted Ni5Ce2/ZSM-5, respectively. Thus, the best results are observed on Ni5Ce2/ZSM-5 and an optimal H2/CO ratio of 0.84 is achieved in this case. Upon decreasing GHSV to 15,000 mL/g.h, CH4 and CO2 conversions jump to 83 % and 88 %, respectively on Ni5Ce2/ZSM-5. Cerium doping produces more desirable strong basic sites and enhances NiO reducibility. This promotes CO2 adsorption and drives the catalytic reaction towards syngas formation, which eventually results in increased efficiency and improved performance.

In situ electrochemical synthesis of atomically dispersed metal sites for efficient hydrogen evolution reaction

In situ electrochemical synthesis of atomically dispersed metal sites for efficient hydrogen evolution reaction

Ni-Co Bimetallic Catalysts Supported on Mixed Oxides (Sc-Ce-Zr) for Enhanced Methane Dry Reforming.

Dry methane reforming (DRM) presents a viable pathway for converting greenhouse gases into useful syngas. Nevertheless, the procedure requires robust and reasonably priced catalysts. This study explored using cost-effective cobalt and nickel combined into a single catalyst with different metal ratios. The reaction was conducted in a fixed reactor at 700 °C. The findings indicate that the incorporation of cobalt significantly enhances catalyst performance by preventing metal sintering, improving metal dispersion, and promoting beneficial metal-support interactions. The best-performing catalyst (3.75Ni+1.25Co-ScCeZr) achieved a good conversion rate of CH4 and CO2 at 46.8 %, and 60 % respectively after 330 minutes while maintaining good stability. The TGA and CO2-TPD analysis results show that the addition of Co to Ni reduces carbon formation, and increases the amount of strong basic sites and isolated O2- species, and the total amount of CO2 desorbed. These results collectively highlight the potential of cobalt-nickel catalysts for practical DRM applications and contribute to developing sustainable energy technologies.

Machine learning-guided design of direct methanol fuel cells with a platinum group metal-free cathode

Direct methanol fuel cells (DMFCs) offer a promising solution for clean electricity generation, particularly in small electronics and remote auxiliary power units. However, optimizing their efficiency and performance is challenging due to the complex interactions between various factors. Here, we present a novel approach that integrates experiments with machine learning to model and predict the performance of these fuel cells using atomically dispersed platinum group metal (PGM)-free catalysts at the cathode. Our machine learning models, trained on diverse input parameters, allow for the comprehensive optimization of DMFC performance prior to fabrication and testing. Through extensive experimental validation, we demonstrate that this data-driven approach accurately predicts key performance metrics, such as maximum power output and polarization curves. By combining our models with interpretable game-theory methods, we provide deep insights into the factors governing fuel cell performance, ultimately paving the way for the design of scalable and efficient DMFC technologies.

Boosting hydroisomerization of n-hexadecane by designing core-shell bifunctional catalysts with partially blocked micropores

Hydroisomerization of long-chain n-alkanes is an indispensable route for upgrading fossil fuels and lubricant oils to meet the state of art regulations. Precisely regulate the distribution of acidic and metal active sites to suppress unwanted cracking reaction is hitherto a difficult task. In this work, we develop a simple coating-carbonation strategy for constructing novel core-shell bifunctional catalysts, comprising ZSM-22 zeolite core with the partially blocked channels and Pt nanoparticles loaded on the mesoporous SiO2 shell. The unique treatment not only adjusted the distribution of acid sites located within the micropore channels and external surface, but also alter the locations and dispersion of Pt nanoparticles. Owing to the short diffusion lengths, nanoscale distance between acid sites and Pt species, and high metal dispersions, the core-shell bifunctional catalyst exhibits outperformed performance in n-hexadecane hydroisomerization, i.e., the yield of isomerized hexadecane can reach 87.9 %, which is among the relatively high level compared with the previous reported Pt/zeolite counterparts. Moreover, the catalyst also displays excellent stability (no deactivation within 100 h). The disclosed structure-catalysis relationship provides rational reference for designing the synergistic meta-acid active sites in the hydroisomerization of long-chain n-alkanes.

Enhancement of CO2 adsorption and oxygen transfer properties on γ-Al2O3 support through surface modification with MgO-ZrO2 for coke suppression over Ni catalyst in CO2 reforming of methane

This work focuses on employing commercial γ-Al2O3 for surface modification with MgO-ZrO2 mixed oxide to enhance the potential of CO2 adsorption and oxygen mobility. This enhancement facilitates its application as a support in catalysts for CO2 utilization such as CO2 reforming of methane (CRM). To achieve this perspective, γ-Al2O3 was modified with 10 wt.% of various MgO and ZrO2 contents (MgO:ZrO2= 10:0, 9:1,7:3, 5:5, 3:7, 1:9 and 0:10) using the impregnation method. All samples including unmodified γ-Al2O3 (Al) were characterized. Due to the increase in basicity and oxygen transfer around the surface, the improvement of the CO2 adsorption was observed on γ-Al2O3 modified with 9 wt.% MgO-1 wt.% ZrO2 (9Mg1ZrAl) and 10 wt.% MgO (10MgAl), respectively. An application of these two superior samples as a support of 10 wt.% Ni (10Ni) catalysts for CRM was investigated and compared with an unmodified γ-Al2O3. Characterization results suggest the formation of NiO-MgO solid solution at the surface due to the decrease in metal-support interaction and the increase in metal dispersion. The Ni catalysts with the surface-modified support show higher CO2 activity that raises carbon deposition resistance. The greatest coke prevention was observed on 10Ni/9Mg1ZrAl that lowers the coke deposition by 42 % compared to 10Ni/Al. It indicates that the composition of this modification allowed very low ZrO2 portion to merge with MgO and MgO to form solid solution with NiO. This enables the 10Ni/9Mg1ZrAl catalyst to generate labile oxygens which can be conveyed to the Ni metal sites on the catalyst.

Estimating Dust Attenuation from Galactic Spectra. III. Radial Variations of Dust Attenuation Scaling Relations in MaNGA Galaxies

We investigate the radial dependence of the scaling relations of dust attenuation in nearby galaxies using integral field spectroscopy data from MaNGA. We identify ionized gas regions of kiloparsec size from MaNGA galaxies, and for each region we estimate both the stellar attenuation E(B − V)star and gas attenuation E(B − V)gas. We then quantify the correlations of 15 regional/global properties with E(B − V)gas and E(B − V)star, using both the feature importance obtained with the Random Forest regression technique and the Spearman correlation coefficients. The importance of stellar mass, metallicity, and nebular velocity dispersion found previously from studies based on the Sloan Digital Sky Survey can be reproduced if our analysis is limited to the central region of galaxies. The scaling relations of both E(B − V)gas and E(B − V)star are found to vary strongly as one goes from the galactic center to outer regions, and from Hα-bright regions to Hα-faint regions. For E(B − V)gas, [N ii]/[S ii] is top-ranked with a much higher correlation coefficient than any other property at 0 < R ≲ R e , while [O iii]/[O ii] outperforms [N ii]/[S ii] as the leading property in the outermost region. For E(B − V)star, stellar age shows the strongest correlation with no/weak dependence on radial distance, although ΣHα and specific star formation rate present similarly strong correlations with E(B − V)star in the galactic center. We find Hα-bright regions to generally show stronger correlations with E(B − V)gas, while Hα-faint regions are more strongly correlated with E(B − V)star, although this depends on individual properties and radial distance. The implications of our results for studies of high-z galaxies are discussed.