Metal Crystallite Size Research Articles

Exploring the preparation of Ni/TiCSiC catalysts for hydrogen production from ammonia

This work explores an innovative and effective approach to address the climatic challenges by designing efficient, novel, and stable nickel catalysts based on a commercial TiCSiC composite as a support material. Through a simple wet impregnation synthesis, these catalysts were successfully synthetized, enabling completely COx-free hydrogen production from ammonia decomposition. To comprehensively understand the nature of the prepared catalyst, a complete characterization was performed. Results revealed that a pretreatment in air at 700 °C optimized catalyst performance, attributed to the TiO2 species emerged in the crystalline structure of the composite and its optimal crystallite size. Moreover, the nickel content affected the metal crystallite size and reducibility and, consequently, the ammonia conversion at moderate temperatures. Thus, the selected catalyst required only 5 wt% of Ni after a calcination in air at 700 °C, converting a notable 91.5 % of ammonia at 500 °C with a hydrogen production rate of 61.3 mmol H2·gNi−1·min−1. The optimized catalyst also demonstrated a long-term thermal stability after more than 45 h in ammonia reactions. These promising findings not only improve catalytic efficiency in current green hydrogen technology, but also contribute significantly to transition towards a sustainable future by using hydrogen vectors and non-critical metals as active phase of catalysts.

Dry reforming of methane at high temperature and elevated pressure over nickel spinellized powder catalyst and pellets prepared from a metallurgical residue

AbstractThe coke deposition on catalysts is a significant problem in the dry reforming of methane at elevated pressures. Understanding and controlling the mechanisms of such deposition is essential in developing a techno‐economically viable industrial application for the production of synthesis gas and/or hydrogen. The patent‐pending nickel‐supported upgraded slag oxide (Ni‐UGSO) catalysts, in powder form, have demonstrated excellent performance and achieved equilibrium in dry reforming, steam reforming and mixed methane reforming in a gram‐scale laboratory packed bed reactor under barometric pressure. In this extended study, Ni‐UGSO pellets were prepared using the wet impregnation method. The pelletized form of said catalyst was studied under elevated pressure to imitate the industrial operating conditions in a kilogram‐scale laboratory packed bed reactor. The characterization of the fresh and used catalytic formulation produced data allowing the investigation of the physicochemical properties of catalysts and the effects of metal dispersion, reaction pressure and crystallite size, as well as the role of side reactions on the nature of the coke. The metal support nature favored the interaction between the Ni metal and spinels (UGSO), and the presence of the clay binder (kaolinite, quartz) improved the pellet morphology, provided higher Ni dispersion, maintained the crystallite size, reduced the coke formation and achieved similar or higher performance with respect to Ni‐UGSO powder despite having 85% less surface area. The Ni‐UGSO pellet showed negligible coke deposits from 1 to 6.5 atm and operated successfully for 24 h at 5.5 atm, 800°C and gas hourly space velocity 810 L/(h kg cat). This study provides new insight into the design of a more efficient and robust catalyst for methane dry reforming at elevated pressures, which is critical for potential future transfer at the industrial level.

Synthesis and characterization of Co3O4, CuO and NiO and nanoparticles: Evaluation of structural, vibrational, morphology and thermal properties

Green synthesis of CuO, NiO, and Co3O4 nanoparticles used biowaste (Gomutra). The physicochemical properties of metal oxide nanoparticles have been studied using various methods. Green synthesised metal oxide nanoparticle crystal properties were calculated using X-ray diffraction. It shows that all metal oxide crystallite sizes are nanoscale (27–31 nm). XRD spectra of CuO nanoparticles confirm their monoclinic structure, which matches JCPDS data. FTIR spectra reveal the existence of functional groups and associated vibrational modes in NiO and Co3O4 nanoparticles, confirming a cubic crystal structure with lattice parameters of 4.175 Å and 8.054 The surface appearance and particle size of three metal oxide nanoparticles were examined by SEM and TEM. XRD matches the average particle sizes of three metal oxide nanoparticles, which are 33–40 nm. Thermal stability of synthesized metal oxide nanoparticles was measured from 0 to 1000 °C using TG-DTA. It shows that the nanoparticles are stable and suited for various applications. Their unique properties make these metal oxide nanoparticles excellent for gas detection, antibacterial activity, photocatalysis, and biosensing.

Influence of the type of support on the physicochemical properties of cobalt catalysts

The article presents the results of studies of the physicochemical properties of cobalt catalysts on a zeolite support. For research, BET methods were used. The nature of the influence of the nature of the support on the structural (specific surface area, dispersion of metal cobalt, size of metal crystallites) and chemical (degree of cobalt reduction) properties of catalysts has been established.

Enhancement of Metal Nanostructure Deposition on Silicon Laser-Induced Periodic Surface Structures by Galvanic Replacement.

We report a chemically motivated, single-step method to enhance metal deposition onto silicon laser-induced periodic surface structures (LIPSSs) using reactive laser ablation in liquid (RLAL). Galvanic replacement (GR) reactions were used in conjunction with RLAL (GR-RLAL) to promote the deposition of Au and Cu nanostructures onto a Si LIPSS. To increase the deposition of Au, sacrificial metals Cu, Fe, and Zn were used; Fe and Zn also enhanced the deposition of Cu. We show that the deposited metal content, surface morphology, and metal crystallite size can be tuned based on the difference in electrochemical potentials of the deposited and sacrificial metal. Compared to the Au and Cu reference samples, GR more than doubled the metal content on the LIPSS and reduced metal crystallite sizes by up to 20%. The ability to tune the metal content and crystalline domain size simultaneously makes GR-RLAL a potentially useful approach in the manufacturing of functional metal-LIPSS materials such as surface-enhanced Raman spectroscopy substrates.

ELECTROSYNTHESIS OF CATALYTIC ACTIVE Pd-Cu AND Pd-Au BIMETALLIC NANOPARTICLES NANOCOMPOSITES WITH POLY(N-VINYLPYRROLIDONE) AND NANOCELLULOSE

It was investigated the preparation in an undivided cell of Pd-Cu and Pd-Au bimetallic nanoparticles (NPs) by methylviologen (MV2+) -mediated electrochemical reduction of equimolar amounts of Cu(II), Pd(II) and Au(I) in the presence of poly(N-vinylpyrrolidone) (PVP) and nanocellulose (NC) at controlled potential of generating MV cation radical in aqueous medium at room temperature. Electrosyntheses were performed by sequential or joint reduction of metal ions by passing a theoretical amount of electricity. When Pd(II) ions are added to CuNPs, as well as Au(I) ions are added to PdNPs, a galvanic replacement process is observed, namely oxidation of Cu0 by Pd(II) and Pd0 Au(I) ions. The results of complete reduction are nanocomposites of mainly spherical MNPs, dispersed in the solution bulk, and stabilized by PVP on the surface of the NC. In the sequential synthesis of CuNPs and then PdNPs, the nanocomposite is presented as Cu2O nanoroses coated with fine PdNPs. Nanocomposites of Pd NPs with Cu2O or Au shows the mainly formation of spherical particles with the size of 4 to 50 nm depending on the production method. X-ray powder diffraction (XRD) data of nanocomposites confirm the formation of a mixture of PdNPs (0.8 - 10 nm) with large gold crystallites (until 24 nm), as well as the oxidation of CuNPs to cuprite (Cu2O). The size of metal crystallites and copper oxide varies in the range from 0.8 to 24 nm. In the test reaction of p-nitrophenol reduction with sodium borohydride in aqueous medium, all tested nanocomposites showed time-increasing catalytic activity. When Cu is added to Pd, the catalytic reduction reaction is maintained, while the addition of Au to Pd decreases the catalytic activity of PdNPs by an order of magnitude.

Hydrogenation of Carbon Monoxide in the Liquid Phase: Influence of the Synthetic Methods on Characteristics and Activity of Hydrogenation Catalysts

Oxygenate fuels are a promising solution to urban air pollution, reducing soot emissions by big margins. Formaldehyde is a major building block for the synthesis of oxygen-rich fuels. Herein we report the synthesis, characterisation and testing of ruthenium on alumina catalysts for the methanol-mediated CO hydrogenation towards oxygenates with the formaldehyde oxidation state. We varied the synthesis parameters and could see interesting correlation between synthesis parameters, final metal loading, crystallite sizes and catalyst activity. The catalysts were tested in a high-pressure three-folded reactor plant in the CO hydrogenation in methanolic media. Interesting relationships between catalyst synthesis, structure and activity could be gained from these experiments.

Boosting hydrogen production by ethanol steam reforming on cobalt-modified Ni–Al2O3 catalyst

Ethanol steam reforming (ESR) is one of the most promising reliable and recyclable technologies for hydrogen production. However, the development of robust, efficient Ni-based catalysts that minimize metal sintering and carbon deposition remains a key challenge. The influence of cobalt loading and ESR conditions on H2 selectivity and catalytic stability is the focus of this study. Ni–Co/Al2O3 catalysts with various Co percentages were prepared by the co-impregnation method and complementary characterization tests were performed. Among the catalysts tested, Ni–Co/Al2O3 (5 wt% Co) exhibited the smallest metal crystallite size, the highest surface area, and the best catalytic performance. Thereafter, the effects of temperature, LHSV and S:C molar ratio were studied. 100% ethanol conversion and maximum H2 selectivity (95.14%) were reached at 600 °C, 0.05 L/gcat.h and S:C molar ratio of 12:1. Furthermore, ethanol turnover frequency (TOF) was computed for each catalyst. TOF results showed that the Ni–Co interaction had an impact on the catalytic activity. Finally, Ni2CoAl was subjected to 50-h stability test and only 6.12 mgcarbon/gcat.h coke deposition was observed.

The synergistic role of Ni-Co bimetallic catalyst for H2-rich syngas production via glycerol dry reforming

A by-product of biodiesel manufacturing, glycerol, is known for its potential to generate syngas via the glycerol dry reforming (GDR) reaction. This study evaluates monometallic and bimetallic Nickel–Cobalt (Ni–Co) (with 15%Co, 3%Ni–12%Co, 4.5%Ni-10.5%Co, 7.5%Ni-7.5%Co, 10.5%Ni-4.5%Co and 15%Ni loading) on Alumina (Al2O3) support extracted from aluminium dross. The catalysts were prepared using an ultrasonic-assisted impregnation process and used in GDR at temperatures ranging from 873 to 1173 K at stoichiometric feed ratio. Analyses result showed that the diluting impact of Ni–Co bimetallic precursors resulted in a reduction of metal crystallite size and improved H2 and CO2 uptake. The conversion of glycerol and product yield were in the order of 3%Ni–12%Co/Al2O3 > 4.5%Ni-10.5%Co/Al2O3 > 7.5%Ni-7.5%Co/Al2O3 > 10.5%Ni-4.5%Co/Al2O3 > 15%Co/Al2O3 > 15%Ni/Al2O3, with 3%Ni–12%Co/Al2O3 having values of 75.6%, 64.7% and 44.8%, for glycerol conversion, H2 and CO yield respectively. All catalysts achieved product ratios ranging from 1.20 to 1.44. The high oxygen vacancies in Ni–Co bimetallic catalysts aided the reduction of carbon formation. Enhanced Ni–Co particles dispersion on Al2O3 support reduced the agglomeration of metal particles, thus, creating smaller crystallite size. The changes in binding energy peaks of Ni and Co were indicative of strong electronic interaction which created Ni–Co bimetallic alloys. 3%Ni–12%Co was regarded as the best catalyst for this study since it was effective in enhancing the conversion of glycerol and product yield.

Characterizations of Ni-loaded lignite char catalysts and their performance enhancements to catalytic steam gasification of coal

Catalyst characteristics such as specific surface area, porosity and active site play an essential role in catalyst design. Understanding of the characteristic functions in controlling catalyst activity is necessary for considering the catalyst application, especially the Ni-loaded lignite char catalyst, employed in catalytic steam gasification. In this work, the unmodified and five modified catalysts were used to study the effect of catalyst characteristics on their performance for catalytic steam gasification of coal in the two-stage fixed-bed reactor. The findings indicated that the fresh acid modified catalysts increased specific surface area and micropore formation, including the smaller Ni metal crystallite size, the decreasing of Ni metal nanoparticle size and the well-dispersed of Ni metal nanoparticles. Meanwhile, the fresh modified catalysts by the alkali and the combined alkali-acid treatments promoted mesopore formation. Enhancing catalytic steam gasification of coal, it was found that the mesoporosity of catalyst was the considerable initial characteristic for controlling the catalyst activity. The total gas yields of the mesoporous catalysts were in the range of 50.65–77.70 mmol/gVM,feed, while the total gas yields of the microporous catalysts were 43.82–55.34 mmol/gVM,feed. After catalyst testings, the specific surface areas and number of mesopores in the spent catalysts were increased by steam. Remarkably, these changing pore sizes affected the transformations of the isotherms (type I + II to type II) and the hysteresis loops (type H4 to type H3). Also, steam influenced the conversion of Ni metals to NiO, Ni(OH)2 and Ni2O3. For thermal property, all spent catalysts had high thermal stability. The modified catalysts could decrease carbon deposition more than the unmodified catalyst, which was an upside for catalyst reusability.

Physicochemical characteristics of calcined MnFe2O4 solid nanospheres and their catalytic activity to oxidize para-nitrophenol with peroxymonosulfate and n-C7 asphaltenes with air

Manganese ferrite solid nanospheres (MSNs) were prepared by a solvothermal method and calcined at various temperatures up to 500 °C. Their surface area, morphology, particle size, weight change during calcination, surface coordination number of metal ions, oxidation state, crystal structure, crystallite size, and magnetic properties were studied. The MSNs were used as catalysts to activate potassium peroxymonosulfate (PMS) for the oxidative degradation of para-nitrophenol (PNP) from water and for the oxidation of n-C7 asphaltenes in flowing air at atmospheric (0.084 MPa) and high pressure (6 MPa). Mn was in oxidation states (II) and (III) at calcination temperature of 200 °C, and the crystalline structure corresponded to jacobsite. Mn was in oxidation states (III) and (IV) at 350 °C and in oxidation states (II), (III), and (IV) at 500 °C, and the crystalline structure was maghemite at both temperatures. MSN catalysts generated hydroxyl (HO·) and sulfate (SO4·-) radicals in the PMS activation and generated HO· radicals in the n-C7 asphaltene oxidation. In both reactions, the best catalyst was MSN calcined at 350 °C (MSN350), because it has the highest concentration of Mn(III) in octahedral B sites, which are directly exposed to the catalyst surface, and the largest total and lattice oxygen contents, favoring oxygen mobility for Mn redox cycles. The MSN350 sample reduces the decomposition temperature of n-C7 asphaltenes from 430 to 210 °C at 0.084 MPa and from 370 to 200 °C at 6.0 MPa. In addition, it reduces the effective activation energy by approximately 77.6% in the second combustion (SC) region, where high-temperature oxidation reactions take place.

Development of nanosilica-based catalyst for syngas production via CO2 reforming of CH4: A review

The alarming global warming issue has sparked interest in researchers to mitigate greenhouse gas emissions via CO2 reforming of CH4 (CRM). Regrettably, the main drawback of CRM is catalyst deactivation because of coking and metal sintering. Therefore, exceptional resistance towards coking and sintering is crucial to formulate viable CRM catalysts. This article reviewed the latest development of nanosilica-based catalysts (mesoporous nanosilica, dendritic fibrous nanosilica, green nanosilica, and core@shell nanosilica) for CRM application. The physicochemical properties of nanosilica supports could be modulated by synthesis methods to improve their resistance towards coking and sintering. Furthermore, this review compiled the influence of catalytic properties of nanosilica supported catalysts, such as active metal dispersion, crystallite size, acid-basic properties, oxygen mobility, reducibility, porosity, and morphology on CRM. To conclude, nanosilica supports with strong metal-support interaction, homogeneous metal dispersion, appropriate crystallite size, and moderate acidity/basicity, exhibited satisfactory catalytic activity, thermal stability, and resistance towards coking and sintering. The fundamental study and depth understanding on this catalysis field is of worth in configuring robust catalysts for future industrial applications success of CRM reaction with superb activity and carbon resistance for CRM.

Hydrogen production from glycerol dry reforming over Ag-promoted Ni/Al2O3

Abstract In recent times, glycerol has been employed as feedstock for the production of syngas (H2 and CO) with H2 as its main constituent. This study centers on dry reforming of glycerol over Ag-promoted Ni/Al2O3 catalysts. Prior to characterization, the catalysts were synthesized using the wet impregnation method. The reforming process was carried out using a fixed bed reactor at reactor operating conditions; 873–1173 K, carbon dioxide to glycerol ratio of 0.5 and gas hourly space velocity (WHSV) in the range of 14.4 ≤ 72 L gcat−1 h−1). Ag (3)-Ni/Al2O3 gave highest glycerol conversion and hydrogen yield of 40.7% and 32%, respectively. The optimum conditions which gave highest H2 production, minimized methane production and carbon deposition were reaction temperature of 1073 K and carbon dioxide to glycerol ratio of 1:1. This result can attributed to the small metal crystallite size characteristics possessed by Ag (3)–Ni/Al2O3, which enhanced metal dispersion in the catalyst matrix. Characterization of the spent catalyst revealed the formation of two types of carbon species; encapsulating and filamentous carbon which can be oxidized by O2.

CeO2 Promoted Ni-MgO-Al2O3 nanocatalysts for carbon dioxide reforming of methane

In this study, the catalytic performance of the CeO2 promoted Ni-MgO-Al2O3 catalysts with different preparation methods was studied in carbon dioxide reforming of methane (CDRM) for the production of synthesis gas. The nitrogen adsorption/desorption (BET), X-ray diffraction (XRD), temperature-programmed reduction and oxidation (TPR and TPO), scanning electron microscopy (SEM) techniques were used to characterize the samples. The obtained results showed that the Ce addition to Ni-MgO-Al2O3 catalyst with the high specific surface area has a significant influence on the metal crystallite size, reduction properties, and coke deposition. The CeO2-Ni-MgO-Al2O3 catalyst with cerium content of 3 wt.% prepared by the impregnation method possessed the highest resistance against carbon formation in CDRM. In addition, the catalytic results confirmed that the feed ratio (CO2/CH4) and GHSV affected the catalytic activity. However, the CH4 and CO2 conversions improved when the cerium was added to Ni-MgO-Al2O3 catalysts.

Supercritical water gasification of glucose using bimetallic aerogel Ru-Ni-Al2O3 catalyst for H2 production

Hydrogen production from biomass using supercritical water gasification (SCWG) is gaining considerable attention as a sustainable source for emerging energy needs. A significant problem with SCWG is the low activity of conventional catalysts with simultaneous graphitic coke formation on the catalyst surface. In this contribution, novel bimetallic nickel-ruthenium supported on alumina catalysts were synthesized via a sol–gel process followed by scCO2 drying (aerogel catalyst). In order to investigate the effect of both Ru and the drying step, both supercritical and conventional drying (xerogel catalyst) were compared with and without Ru. All catalyst types were examined for glucose gasification in supercritical water using a 600 cm3 batch reactor from 400 to 500 °C at 25 to 35 MPa. The fresh and spent catalysts were then characterized by various physico-chemical techniques to understand the role of Ru and the deactivation mechanism. Ru-Ni-Al2O3 aerogel catalyst reduced graphitic coke formation, significantly enhancing H2 formation while also increasing the carbon gasification efficiency (CGE) and total organic carbon (TOC) destruction, respectively. H2 yield was increased 1.7 times higher for Ru-Ni-Al2O3 aerogel compared to the xerogel. Ni-Al2O3 aerogel and impregnated catalyst provided 1.26 and 1.55 times lower H2 yield compared to Ru-Ni-Al2O3 aerogel catalyst. This is attributed to the Ru-Ni-Al2O3 aerogel catalyst having a higher BET surface area as well as larger pore volume, smaller active metal crystallite sizes, and a higher degree of active metal dispersion.

Hydrogenation of CO2 over supported noble metal catalysts

The catalytic activity of supported noble metal catalysts for the CO2 methanation reaction has been investigated with respect to the nature (Rh, Ru, Pt, Pd), loading (0.1–5.0wt.%) and mean crystallite size (1.3–13.6nm) of the dispersed metallic phase. It has been found that the turnover frequency (TOF) of CO2 conversion for TiO2-supported catalysts increases following the order of Pd<Pt<Ru<Rh, with Rh being about 3 times more active than Pd. Selectivity toward methane depends strongly on the noble metal catalyst employed and is significantly higher for Rh and Ru catalysts compared to Pt and Pd, which mainly promote production of CO via the RWGS reaction. Conversion of CO2 at a given temperature increases significantly with increasing Ru loading in the range of 0.1–5.0wt.%. Results of kinetic measurements show that the CO2 hydrogenation reaction is structure sensitive, i.e., catalytic activity is strongly influenced by metal crystallite size. In particular, for Ru/TiO2 and Ru/Al2O3 catalysts, the normalized turnover frequency (TOF divided by the length of the perimeter of the metal-support interface) increases by two orders of magnitude with increasing ruthenium crystallite size in the range of 0.9–4.2nm and 1.3–13.6nm, respectively. FTIR experiments provide evidences that CO2 hydrogenation reaction occurs via intermediate formation of adsorbed CO species (Rux-CO, Run+(CO)x, (TiO2)Ru-CO) produced via the RWGS reaction. Part of this species interacts with adsorbed hydrogen atoms producing methane, whereas the remaining species desorbs to yield CO in the gas phase. The CO2 hydrogenation pathway does not change with variation of Ru crystallite size. However, the relative intensity of the band due to CO species linearly bonded on reduced Ru crystallites (Rux-CO) increases significantly with increasing Ru particle size, indicating that Rux-CO species could potentially being the reactive surface intermediates.

Operando Synchrotron XRD Investigation of Silver Metal Formation upon Electrochemical Reduction of Silver Iron Pyrophosphate (Ag7Fe3(P2O7)4)

The formation of conductive metallic silver upon electrochemical reduction and lithiation of Ag7Fe3(P2O7)4 is investigated. Alternating current impedance spectroscopy measurements show a 34% decrease in charge transfer resistance upon one electron equivalent (ee) of reduction, which is coincident with the formation of a Ag metal conductive network evidenced by both ex situ and operando X-ray diffraction. Quantitative assessment of Ag metal formation derived from operando XRD shows that only Ag+ ions are reduced during the first 3ee, followed by simultaneous reduction of Ag+ and Fe3+ reduction for the next 5ee (3ee to 8ee), culminating in reduction of the remaining Ag+. Scanning electron microscopy images show smaller Ag metal crystallite size and shorter nearest neighbor distance between and among Ag particles with higher depth of discharge. A high rate intermittent pulsatile discharge test is conducted where the cell delivers 12 total pulses during full discharge to probe the effect of Ag metal formation on the Li/Ag7Fe3(P2O7)4 cell electrochemistry. The Ohmic resistance is derived from the voltage drop of each pulse. The resistance is 65 Ω initially, reaches its minimum of 26 Ω at 4.5 ee discharge, and levels off at 35 Ω after 7.0 ee reduction. The initial Ag reduction is more significant for the conductive network formation indicated by the decrease of both Rct and Ohmic resistance, which facilitates the high power output of the cell.

Mechanistic Study of the Selective Methanation of CO over Ru/TiO2 Catalysts: Effect of Metal Crystallite Size on the Nature of Active Surface Species and Reaction Pathways

The effect of metal crystallite size on the reaction mechanism of competitive methanation of CO and CO2 is investigated over Ru/TiO2 catalysts of variable metal content (0.5 and 5.0 wt %) and crystallite size (2.1 and 4.5 nm) employing in situ FTIR and transient mass spectrometry techniques. Results show that although both catalysts follow the same mechanistic pathways, the relative population of reaction intermediates differs. Specifically, the nature of Ru-bonded carbonyl species detected on the catalyst surface upon interaction with the CO/CO2-containing gas mixtures is the same for both catalysts. However, their relative population depends significantly on ruthenium crystallite size and determines catalytic activity. The population of multicarbonyl species adsorbed on partially oxidized Ru sites (Run+-(CO)x) decreases significantly with increasing Ru crystallite size, whereas the opposite is observed for CO species linearly bonded on reduced Ru crystallites (Rux-CO). This is correlated with the higher...

Improvement of Cobalt Dispersion on Co/SBA-15 and Co/SBA-16 Catalysts by Ultrasound and Vacuum Treatments during Post-Impregnation Step

The Co/SBA-15 and the Co/SBA-16 catalysts having 20 wt% of cobalt were prepared by the conventional impregnation method. Then, the post-impregnation treatments including vacuum and ultrasound treatments were applied. The synthesized catalysts were characterized by means of N 2 physisorption, small angle X-ray diffraction (SAXRD), wide angle X-ray diffraction (XRD), scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM/EDX), transmission electron microscopy (TEM), and temperature-programmed reduction (TPR). The results show that the synthesized SBA-15 had hexagonal structure and the synthesized SBA-16 had the cubic structure. The vacuum and the ultrasound treatments after incipient wetness impregnation can apparently enhance the dispersion of cobalt on the SBA-15 catalysts due to the decrease of the metal crystallite size. However, only the vacuum treatment was suitable for the Co/SBA-16. After reduction, no cobalt-silicate compound was detected based on XRD measurement. Both post-impregnation treatments can also decrease the metal-support interaction resulting in increased activity for CO 2 hydrogenation under methanation.

SO2 adsorption and desorption characteristics of Pd and Pt catalysts: Precious metal crystallite size dependence

SO2 adsorption and desorption on Pt/Pd mono- and bimetallic, γ-Al2O3 supported catalysts were characterized. There are dependencies on both particle size and Pd:Pt ratio, and here particle size effects on the adsorption and desorption trends and surface species formed were evaluated using DRIFTS and TPD studies. Catalysts with a smaller particle size tended to form a greater amount of aluminum sulfate species, which decomposed at high-temperature. In contrast, catalysts with larger particle sizes tended to form a greater amount of low-temperature decomposing and desorbing species, such as molecular SO2 and surface aluminum sulfite. In general, it was found that the amount of SO2 adsorbed and later desorbed during TPD decreased with increasing particle size.