Conventional Impregnation Method Research Articles

Supercritical solvothermal synthesis under reducing conditions to increase stability and durability of Mo/ZSM-5 catalysts in methane dehydroaromatization

Natural gas is currently envisioned as a potential energy and hydrocarbon feedstock in the forthcoming years. To overcome the detrimental flaring of this natural gas and the partial release of its major component, methane, novel and more effective strategies are required. These include the development of new, efficient and seemingly stable catalysts able to rapidly convert methane into valuable feedstocks. We show a novel synthesis method of Mo/ZSM-5 based on a solvothermal synthesis under supercritical conditions and reducing atmosphere (SC-STS-E) to improve metal dispersion and enhance catalyst stability and durability during the methane dehydroaromatization (MDA) reaction. In contrast to the conventional impregnation method, SC-STS-E provides a super-high atom-like metal dispersion at the zeolite pores resulting in the most stable Mo/ZSM-5 catalyst for MDA with the highest long-term hydrocarbon yield (xCH4 = 11.6% and yC2+ = 8.9%, after 15 h on stream) among the catalysts reported in literature for this reaction.

Preparation of Ag-Mn/γ-Al2O3-TiO2 catalysts by complexation-impregnation process with citric acid and its application in propane catalytic combustion

A series of Ag-Mn/γ-Al2O3-TiO2 catalysts were prepared by different impregnation procedures. The catalysts were characterized by BET, XRD, TEM, XPS and H2-TPR, and the catalytic properties were investigated by propane catalytic combustion. Results show that compared with the conventional impregnation method, complexation-impregnation procedure with citric acid promotes the dispersion of Ag and Mn particles on the surface of catalyst and strengthens the interaction between Ag and Mn, so as to increase the relative content of reactive oxygen species and improve the reducibility of catalysts, which further improves the catalytic activity of propane combustion reaction. Especially, the Ag1Mn3/γ-Al2O3-TiO2 catalyst prepared by complexation-impregnation process with citric acid exhibits the best activity for propane catalytic combustion with 90% conversion at 263°C.

Hydroxyapatite as a new support material for cobalt-based catalysts in Fischer-Tropsch synthesis

Hydroxyapatite [HAP, (Ca10(PO4)6(OH)2)] is an emerging catalytic support possessing exciting features such as high thermal and mechanical strength, chemically stable with low water solubility along with tunable porosity and acid-basic character. Despite of these interesting characteristics, it has not yet been investigated in Fischer-Tropsch (FT) synthesis. Herein, for the first time, HAP-supported cobalt catalysts (Co/HAP) prepared by conventional incipient wetness impregnation method were examined in the FT synthesis process. The catalytic performance of these catalysts was compared with alumina-supported cobalt catalysts (Co/Alumina). HAP support was found to exhibit considerably less acid-site density, consequently, reducing detrimental interactions of the support with cobalt precursors leading to hardly reducible Co species that are generally observed with its alumina counterpart. Co/HAP catalysts exhibit relatively larger Co particle sizes (~9 nm versus ~6 nm, as observed from TEM analysis) and better Co reducibility when compared to its counterparts on alumina. FT synthesis at 20 bar, 220 °C and H2/CO = 2.1 showed that the CO conversion was higher on the catalysts (10 wt% Co loading) using HAP as a support material when compared to alumina. Under different testing conditions (220 or 230 °C) using the Co/HAP catalyst, the C5+ selectivity was in the range of 82–88%, whereas the methane selectivity was about ~10%.

A versatile approach for quantification of surface site fractions using reaction kinetics: The case of CO oxidation on supported Ir single atoms and nanoparticles

Supported metal single-atom catalysts have shown unique activity and selectivity for several reactions. Investigating the reaction mechanism on single-atom catalysts and unambiguous assignment of the activity and selectivity requires catalysts with exclusively single atoms. However, it is challenging to prepare pure single-atom catalysts with conventional impregnation methods, which typically result in a mixture of single atoms and nanoparticles. Here, we show that owing to different reaction mechanisms on single atoms and nanoparticles, reaction kinetics can serve as a surface sensitive characterization technique for quantifying their surface site fractions. As a case study, we use CO oxidation kinetics on Ir/MgAl2O4 to quantify the surface site fractions of single atoms and nanoparticles and the results are consistent with aberration-corrected scanning transmission electron microscopy, X-ray absorption fine structure and infrared spectroscopies. Additionally, by carefully choosing the reaction conditions, the activity of single atoms (or nanoparticles) can be made dominant, enabling detection of a small fraction, or allowing a study of their reaction mechanism on a catalyst containing a mixture of single atoms and nanoparticles. These results are general and could be applied to other systems where two types of sites have different reaction mechanisms.

Morphological Effects on Surface Oxidation Tolerance of Metallic Nanosheets

Metallic nanosheets have attracted much attention owing to its intrinsically large surface area, highly anisotropic structure, and flexible but rigid structure. Understanding the correlation between activity and stability of metallic nanosheets is necessary to clarify the advantage of two-dimensional morphology. In this work, the activity and stability of metallic Ru nanosheets and nanoparticles were studied to understand the two-dimensional morphological effects on the electrochemical properties, in particular, the tolerance towards surface oxidation. Ru nanosheet supported on carbon (Ru(ns)/C) was prepared by a process reported previously.1 Ru nanoparticles supported on Ketjen black (Ru(np)/C, 2.8±0.3 nm) was synthesized by a conventional impregnation method as a control sample. The ORR mass activity of Ru nanosheets was 1.3 times higher than that of nanoparticles, this is attributed to the larger electrochemically active surface area compared with nanoparticles. The ORR mass activity of nanosheets after 500 potential cycles was 77 A (g-Ru)- 1, which is 39 times higher than that of nanoparticles (Fig. 1(a)). Although the nanoparticles were oxidized by potential cycles (Fig. 1(b)), the nanosheets maintained metallic state. The result suggests that the metallic Ru nanosheets possesses higher tolerance against surface oxidation compared with Ru nanoparticles. Based on the electrochemical measurements, in-situ XAFS analysis, and theoretical simulations, we discuss the cause of the high anti-oxidation properties for Ru nanosheets. The average coordination number of surface for 2.4 nm Ru (hcp) was 5-6.2 On the other hand, the average coordination number of Ru nanosheets was 8, which is higher than that of nanoparticles. This suggests that the Ru nanosheets is thermodynamically stable compared with Ru nanoparticles. The above results suggest that nanoparticles were easily oxidized by potential cycling due to the low coordination number of surface atoms compared to nanosheets. Therefore, the surface oxidation tolerance of Ru nanosheets was higher than that of Ru nanoparticles, and the nanosheet structure should contribute to the improved stability against surface oxidation during potential cycles. This research was supported in part by the “Polymer Electrolyte Fuel Cell Program” from the New Energy and Industrial Technology Development Organization (NEDO) of Japan. References D. Takimoto, T. Ohnishi, J. Nutariya, Z. Shen, Y. Ayato, D. Mochizuki, A. Demortière, A. Boulineau, and W. Sugimoto, J. Catal., 345, 207 (2017).L. S. R. Kumara, O. Sakata, S. Kohara, A. Yang, C. Song, K. Kusada, H. Kobayashi, and H. Kitagawa, Phys. Chem. Chem. Phys., 18, 30622 (2016). Figure 1. (a) Retention in ORR mass activity of Ru(ns)/C (red square) and Ru(np)/C (black circle) as a function of potential cycle number. (b) Pre-adsorbed CO stripping voltammograms of Ru(ns)/C (red) and Ru(np)/C (black) after potential cycles (0.1 M HClO4 (25oC), v = 10 mV s-1). Solid line: 1st cycle after CO adsorption; broken line: 2nd cycle. Figure 1

Enhanced Alkaline Hydrogen Oxidation Reaction by Modifying Pt Nanoparticle Surface with Another Metal

Anion exchange membrane fuel cells (AEMFCs) can reduce the cost of fuel cell systems because they allow the use of non-precious metals in catalysts due to their less corrosive internal environments, which gives them an advantage over conventional proton exchange membrane fuel cells (PEMFCs) with highly corrosive environments. Taking this advantage, non-precious-metal catalysts have been developed in particular for cathode, i.e., for the oxygen reduction reaction (ORR). However, the cell performance of AEMFCs is still inferior to that of PEMFCs. One of the reasons is sluggish hydrogen oxidation reaction (HOR) on anode, as represented by the fact that the HOR rate on Pt catalysts in alkaline conditions is two orders of magnitude slower than that in acidic conditions. It would be reasonable to consider that development of catalysts for the HOR enhances the AEMFC performance. In fact, the previous studies have demonstrated that alloying and size-control of metal nanoparticle catalysts improve the HOR activity and the cell performance. Recently, the cell performance has been getting closer to that of PEMFCs by the improvement of HOR catalysts with the help of the state-of-the-art anion exchange membranes having high ion conductivity. However, a lot of precious metals are needed on AEMFC anode to obtain such high cell performance. Therefore, the HOR catalysts in alkaline conditions have to be further developed for widespread use of AMFCs as an alternative of PEMFCs. Previous studies on the alkaline HOR have suggested two mechanisms accounting for enhancement of the HOR activity: hydrogen-binding-energy (HBE) mechanism and bifunctional mechanism. The HBE mechanism can account for the variation of HOR activity with pH of electrolyte as well as with metal species. The bifunctional mechanism has been recently suggested as another mechanism contributing to the improved HOR kinetics. In the bifunctional mechanism, catalyst surface not only adsorbs hydrogen but also supplies reactive oxygen species to the adsorbed hydrogen. These mechanisms have driven us to modify catalyst surface systematically, because tuning of surface property is expected to change the HBE and/or the reactive oxygen species, and consequently improve the HOR activity based on the bifunctional mechanism. In this paper, we show enhanced or lowered HOR activity of Pt/C by surface modification of Pt nanoparticles with various metals on the group 4-11 of the 4th and 5th period in the periodic table except for Tc, i.e., Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Rh, Pd, Ag (fifteen metals). Commercially available Pt/C (TEK10E50E, Pt 46.7wt%) is modified with the fifteen metals using a conventional impregnation method to load 7.7at% of the metals on Pt/C. The catalysts are denoted as M/Pt/C. The electrochemically active surface area (ECSA) is determined from the electric charge due to HUPD in 0.1 M NaOH aq. saturated with N2. The HOR activity is determined from linear sweep voltammograms obtained using a rotating disk electrode method in 0.1 M NaOH aq saturated with H2 at 25°C. The exchange current (i0) is determined using the approximate Butler-Volmer equation. The mass activity (MA) is determined by dividing i0 by the total amount of Pt and added metals. Interestingly, most M/Pt/C samples presents higher MA values than Pt/C, although the modifying metals are less active than Pt when used individually for the HOR. Thus, modifying Pt/C enhance the HOR on Pt/C. Modification with Co was most effective for enhancing the MA of the metals in the third period, with a MA twice that of Pt/C; Ru in the fourth period exhibited a MA 2.5 times higher than that of Pt/C. It is noteworthy that the MAs of various M/Pt/C samples including Mo, Ru, and Pd/Pt/C are significantly higher than a state-of-the-art Pt-Ru alloyed nanoparticle catalyst (TEC61E54 supplied by Tanaka Kikinzoku Kogyo). The specific activity (SA) of M/Pt/C for the HOR is determined by dividing i0 by the ECSA. The SA varies with a volcano shape on both elemental periods with a peak at Co on the 4th period and at Ru on the 5th period, where the SA value is enhanced two times compared to Pt/C. The mechanism of the enhanced HOR activity is investigated in terms of the hydrogen binding energy (HBE) on catalysts. However, the variation of HOR activity exceeds the effect of HBE, suggesting contribution of bifunctional mechanism. The bifunctional mechanism is supported by volcano-shaped dependence of the SA on the following descriptors for reactivity of surface oxygen species: the standard oxidation potential and the standard formation enthalpy of the modifying metals.

Stable Multimetallic Nanoparticles for Oxygen Electrocatalysis.

Nanostructured catalysts often face an important challenge: poor stability. Many factors contribute to catalytic degradation, including parasitic chemical reactions, phase separation, agglomeration, and dissolution, leading to activity loss especially during long-term catalytic reactions. This challenge is shared by a new family of catalysts, multimetallic nanoparticles, which have emerged owing to their broad tunability and high activity. While significant synthesis-based advances have been made, the stability of these nanostructured catalysts, especially during catalytic reactions, has not been well addressed. In this study, we reveal the critical influence of a synthetic method on the stability of nanostructured catalysts through aprotic oxygen catalysis (Li-O2 battery) demonstrations. In comparison to the conventional wet impregnation (WI) method, we show that the carbothermal shock (CTS) method dramatically improves the overall structural and chemical stability of the catalyst with the same elemental compositions. For multimetallic compositions (4- and 8-elements), the overall stability of the electrocatalysts as well as the battery lifetime can be further improved by incorporating additional noncatalytically active elements into the individual nanoparticles via CTS. The results offer a new synthetic path toward the stabilization of nanostructured catalysts, where additional reaction schemes beyond oxygen electrocatalysis are foreseeable.

Zeolite supported TiO2 with enhanced degradation efficiency for organic dye under household compact fluorescent light

Crystalline zeolite immobilized TiO2 nanoparticles (NPs) were prepared using conventional liquid impregnation (LI) method and were employed to achieve efficient decomposition of basic cationic dye, Methylene Blue (MB). The novel aspect of physical modification (impregnation) with zeolite was found successful to overcome the UV light requirements for photocatalytic reaction involving TiO2. Moreover, the effects of different calcination temperatures i.e. 500, 700 and 900 °C were examined. The composite materials were characterized using SEM/EDX, TEM, XRD, XRF, FTIR, DRS UV–vis and point of zero charge (pHPZC) analyses. The present research indicates that the biphasic nature (anatase = 85% and rutile/brookite = 15%) due to high calcination temperature and the presence of zeolite support enhanced the photocatalytic degradation of MB up to 4 folds as compared to the pure anatase TiO2. The highest photocatalytic removal efficiency for MB under household compact fluorescent light reached to 155 mg l−1 (qm = 62 mg g−1). The effects of technology parameters, such as basic pH and the presence of electron trapper, Cd2+ ions, enhanced the removal efficiencies to maximum. The physical regeneration method exhibited comparatively high degradation efficiency (135 mg l−1 MB removal, qt = 54 mg g−1) after first regeneration.

Design novel inorganic precursors for producing clean fuels by using Fischer-Tropsch synthesis

A new metal-organic framework compound formulated as [Co0.67Zn0.83(btc)(H2O)6] (1) was prepared and characterized by elemental analysis, and FT-IR spectroscopy. The single crystal analysis was used for determination of its structure. The complex was used for the preparation of two inorganic precursors [Co0.67Zn0.83(btc)(H2O)6]/SiO2 and [Co0.67Zn0.83(btc)(H2O)6]/Al2O3, which were thermally decomposed to obtain new Co-Zn alloy catalysts for Fischer-Tropsch synthesis. The same catalysts were prepared by the conventional impregnation method as reference catalysts. The catalysts were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and BET specific surface area, and their catalytic performances were studied in the temperature range 200–300 °C and P = 5 bar. The results show that the Co-Zn synthesized alloy catalysts have acceptable activity in the Fischer-Tropsch (FTS) synthesis and have better selectivity to desired products than reference catalysts. The difference between the Co-Zn alloy catalysts and the reference catalysts is mainly caused by their different particle size.

Enhanced Ni-Al-Based Catalysts and Influence of Aromatic Hydrocarbon for Autothermal Reforming of Diesel Surrogate Fuel

Aromatic hydrocarbons along with sulfur compounds in diesel fuel pose a significant threat to catalytic performances, due mainly to carbon deposition on the catalytic surface. In order to investigate the influence of an aromatic hydrocarbon on the autothermal reforming of diesel fuel, 1-methylnaphthalene (C11H10) was selected as an aromatic hydrocarbon. Two types of diesel surrogate fuel, i.e., DH (dodecane (C12H26) and hexadecane (C16H34) mixture) as well as DHM (DH fuel and C11H10 mixture) fuel, were prepared. A Rh-Al-based catalyst (R5A-I) was prepared using a conventional impregnation method. Various Ni-Al-based catalysts with Fe and Rh promoters were prepared via a polymer modified incipient method to improve the carbon coking resistance. These catalysts were tested under conditions of S/C = 1.17, O2/C = 0.24, 750 °C, and GHSV = 12,000 h-1 at DH or DHM fuel. R5A-I exhibited excellent catalytic performance in both DH and DHM fuels. However, carbon coking and sulfur poisoning resistance were observed in our previous study for the Ni-Al-based catalyst with the Fe promoter, which became deactivated with increasing reaction time at the DHM fuel. In the case of the Rh promoter addition to the Ni-Al-based catalysts, the catalytic performances decreased relatively slowly with increasing (from 1 wt.% (R1N50A) to 2 wt.% (R2N50A)) content of Rh2O3 at DHM fuel. The catalysts were analyzed via scanning electron microscopy combined with energy dispersive X-ray, X-ray diffraction, and X-ray photoelectron spectroscopy. Gas chromatography-mass spectrometry detected various types of hydrocarbons, e.g., ethylene (C2H4), with catalyst deactivation. The results revealed that, among the produced hydrocarbons, C2H4 played a major role in accelerating carbon deposition that blocks the reforming reaction. Therefore, Rh metal deserves consideration as a carbon coking inhibitor that prevents the negative effects of the C2H4 for autothermal reforming of diesel fuel in the presence of aromatic hydrocarbons.

Uniform small metal nanoparticles anchored on CeO2 nanorods driven by electroless chemical deposition

We report a facile electroless chemical deposition (ECD) method to deposit uniform Pd nanoparticles ((2.5 ± 0.6) nm) on CeO2 nanorods (PdNPs/CeO2-ECD) through the interface redox reaction between the reduced CeO2 and Na2PdCl4. PdNPs/CeO2-ECD exhibits a stronger electronic metal–support interaction (EMSI) evidenced by higher reducibility and stronger anti-sintering capability at high temperatures, compared to that prepared by the conventional impregnation method. Such an EMSI effect of PdNPs/CeO2-ECD significantly improves its catalytic activity in CO oxidation. Besides, the chlorine residue-free catalysts through ECD process avoid the deleterious effect of chlorine on CO oxidation. This ECD process can further be extended to deposit various uniform nanoscaled noble metals (Au, Ag, Pt, Ru, Rh, etc.) on CeO2, which may deliver their potentials in advanced catalysis.

Catalytic device on the base of glass-fiber catalyst for environmentally safe combustion of fuels and utilization of toxic wastes

The work is dedicated to development of the optimal glass-fiber catalyst (GFC) for the process of environmentally efficient combustion of hydrocarbon fuels and utilization of organic wastes. The primary selection of catalysts using the test reaction of toluene oxidation in air showed that the best activity and minimum formation of by-products is observed at Pt-containing GFCs. Among them the best efficiency is observed for the GFCs prepared by spraying of active component precursor instead of conventional impregnation method; they are characterized with higher uniformity of active component deposition across the fiber surface and higher dispersion of Pt particles leading to their higher activity, despite lower Pt content. The prototype of the device for combustion of hydrocarbon fuels was made on the base of structured Pt/GFC cartridge. The tests performed with LPG fuel showed the achievement of planned heat power of 15 kW, practical absence of NOx and minimum CO and hydrocarbon content in the combustion products. The developed combustor may be used for direct air heating in various rooms and buildings, as well as for utilization of toxic organic wastes.

Highly dispersed Ni[sbnd]Cu nanoparticles on SBA-15 for selective hydrogenation of methyl levulinate to γ-valerolactone

Copper and nickel nanoparticles highly dispersed on an ordered mesoporous silica support (SBA-15) were prepared by a glycol-assisted impregnation method and tested for the catalytic transfer hydrogenation reaction of methyl levulinate to γ-valerolactone (GVL). Characterizations by high resolution transmission electron microscopy, X-ray diffraction, N2 sorption, H2 temperature-programmed reduction and X-ray absorption spectroscopy confirm that the highly dispersed nanoparticles were well-anchored to the mesopores of SBA-15 with the strong interaction. Comparing to a catalyst synthesized by a conventional aqueous impregnation method, our catalyst shows a higher conversion and greater selectivity towards GVL of reaction at 140–170 °C using 2-propanol as a solvent and a hydrogen donor. Results showed that NiCu/SBA-15 (EG) had much better activity, providing 91.3% conversion of ML with 89.7% selectivity towards GVL in 3 h at 140 °C. The high compositional homogeneity, uniform distribution of the nanoparticles in the mesoporous channels and the strong interaction between the metal nanoparticles and SBA-15 contribute to the superior catalytic performance. This catalyst also demonstrates superb stability over the course of 5 reaction cycles without significant loss in catalytic activity and selectivity towards GVL formation.

Ni-based nano-catalysts for the dry reforming of methane

Abstract Development of a highly efficient and coke-resistant, nickel based nano-catalyst in the carbon dioxide reformation of methane is reported. The alumina supported Ni-based catalyst with a metal loading of 5wt% was prepared via the solution combustion synthesis (SCS) method as well as the conventional wetness impregnation method. The synthesized catalysts were thoroughly characterized by a combination of analytical techniques including high-resolution electron microscopy (HRTEM-SAED), X-ray diffraction (XRD), nitrogen physisorption (BET surface area), X-ray photoelectron spectroscopy (XPS), temperature programmed reduction (H2-TPR) and temperature programmed oxidation (TPO). Compared to the conventional nickel-impregnated (Ni-I) catalyst, the Ni-SCS nano-catalyst was superior in activity and stability during dry reformation of methane. Ni-SCS catalyst exhibited higher percentage conversions of methane and carbon dioxide. The percentage yields of hydrogen and carbon monoxide over Ni-SCS catalyst were also significantly higher. During the investigated period on stream for 50 h, the Ni-I catalyst deactivated severely, by contrast the Ni-SCS stayed active. It was clear from the results of elemental carbon analysis and TPO that deactivation of the Ni-I catalyst was due to severe carbon deposition, whereas the Ni-SCS catalyst exhibited minor carbon deposition. These differences in the catalytic activities and stabilities between the Ni-I and Ni-SCS catalysts were attributed to the difference in their physicochemical properties and chemical structure, as obvious from the results of the above mentioned analysis techniques. The XRD and XPS analysis revealed that the Ni-SCS nanocatalyst resulted in the formation of uniformly distributed nickel aluminates (NiAl2O4) nano-crystallite spinels together with nickel oxide. The results of H2-TPR analysis clearly distinguished between NiO and NiAl2O4. H2-TPR affirmed the formation of NiAl2O4 and NiO species on the SCS nanocatalyst but only NiO within the impregnation catalyst. In this regards the exceptionally high catalytic activity and stability of Ni-SCS nanocatalyst during dry reformation was attributed to the presence of NiAl2O4 nano-crystallites structures. On the other hand, the presence of weakly associated NiO species on the Ni-I catalyst was responsible for decaying its activity due to carbon formation during the dry reformation of methane.

Defect-Rich Nickel Nanoparticles Supported on SiC Derived from Silica Fume with Enhanced Catalytic Performance for CO Methanation

With the increased demands of environmental protection, recycling/utilization of industrial byproducts has attracted much attention from both industry and academic communities. In this work, silicon carbide (SiC) was successfully synthesized from industrial waste silica fume (SF) during metallic silicon production. Following this, Ni nanoparticles with many defects were supported on the as-obtained SiC by conventional impregnation method. The results showed that defect-rich Ni nanoparticles were dispersed onto the surface of SiC. The as-obtained Ni/SF-SiC exhibited an enhanced metal-support interaction between Ni and SiC. Furthermore, the density functional theory (DFT) calculations showed that the H2 and CO adsorption energy on Ni vacancy (VNi) sites of Ni/SF-SiC were 1.84 and 4.88 eV, respectively. Finally, the Ni/SF-SiC performed high catalytic activity with CO conversion of 99.1% and CH4 selectivity of 85.7% at 350 °C, 0.1 MPa and a gas hourly space velocity (GHSV) of 18,000 mL·g−1·h−1. Moreover, Ni/SF-SiC processed good catalytic stability in the 50 h continuous reaction.

Platinum Cocatalyst Loaded on Calcium Titanate Photocatalyst for Water Splitting in a Flow of Water Vapor.

In water splitting by using heterogeneous photocatalysts, the use of a suitable cocatalyst has been recognized as one of the key factors in enhancing the photocatalytic activity. Although platinum is a representative cocatalyst for many heterogeneous photocatalytic reactions, it has not been used for photocatalytic water splitting, owing to its high catalytic activity for the reverse reaction of water splitting. In the present study, platinum nanoparticles were loaded as a cocatalyst on a calcium titanate photocatalyst by a conventional impregnation method and a photodeposition method and examined for photocatalytic water splitting in a flow of water vapor. Platinum nanoparticles loaded by the impregnation method were found to retain the oxidized form on the calcium titanate photocatalyst, even under photoirradiation, and promoted hydrogen and oxygen production by photocatalytic water vapor splitting without promoting the reverse reaction.

The effect of metal loading over Ni/γ-Al2O3 and Mo/γ-Al2O3 catalysts on reaction routes of hydrodeoxygenation of rubber seed oil for green diesel production

Abstract Hydrodeoxygenation (HDO) of vegetable oil is one of the promising key processes designed for a possible convenient method for automotive clean fuel production. The HDO of rubber seed oil into diesel range hydrocarbon over non-sulphided monometallic (Ni/γ-Al2O3 and Mo/γ-Al2O3) catalysts were investigated. The catalysts were synthesized via conventional wet impregnation method using 3 wt.%, 12 wt.% and 15 wt.% Ni and Mo loading over γ-Al2O3 support, to examine the influence of metal loading on catalytic activity, coke deposition, and reaction routes. The synthesized catalysts were subjected to characterization techniques including XRD, FESEM coupled with EDX, BET, TEM, TGA, ICP-OES and H2TPR. All the catalysts were tested for HDO reaction at 623.15 K, 3.5 MPa, H2/oil of 1000 N (cm3/cm3) with WHSV = 1 h−1 in a continuous flow fixed bed tubular reactor. The hydrocarbon products were analyzed using gas chromatography, and intermediates were identified using GC–MS. The Ni supported catalysts showed comparatively higher surface area, small particle size, homogeneous dispersion of particles, higher crystallinity and lower reduction temperature, low coke deposition. Proposed reaction mechanism suggests the decarboxylation (DCO2) reaction occurred mainly over Ni supported catalysts. Whereas, higher Ni loading reduced the extent of decarboxylation (DCO2) reaction. Additionally, Mo supported catalysts allowed the deoxygenation reaction to occur and higher Mo loading enhanced the extent of hydrodeoxygenation (HDO). The triglycerides conversion for all the catalysts was 99.9%. The catalysts with higher metal loading showed overall higher catalytic activity for hydrodeoxygenation of RSO. 15 wt.% Ni loading produced higher hydrocarbon yield (55.1 wt.%) whereas, 15 wt.% Mo loading produced up to 61.7 wt.%. Mo comparatively produced high amount of C16 (15.7 wt.%), and C18 (30.7 wt.%) hydrocarbons. Whereas, Ni produced mainly C15 (20.9 wt.%) and C17 (20.3 wt.%) hydrocarbons. Significant findings were observed on hydrocarbon yield, intermediates, and amount of coke formation. Mo supported catalysts shows significant HDO activity with less concentration of oxygenated component in the mixture. Besides Mo supported catalysts exhibit the high amount of coke deposition compared to Ni supported catalysts.

Unravelling the structure-performance relationship over iron-based Fischer-Tropsch synthesis by depositing the iron carbonyl in syngas on SiO2 in a fixed-bed reactor

A new process, in situ deposition method, was developed to unveil Fe phase evolution behavior in iron-based Fischer-Tropsch synthesis (FTS). In detail, Fe(CO)x-containing syngas (CO/H2) was fed into a fixed-bed reactor where Fe(CO)x directly decomposes to metallic Fe with subsequent favorable carburization to form active χ-Fe5C2 on SiO2 under FTS reaction conditions. This facile process gives a high χ-Fe5C2 content (80–90%) without Fe3O4 phase in spent catalyst. In contrast, the 5.3Fe/SiO2 prepared by the conventional impregnation method results in very low χ-Fe5C2 content (14.5%) and high Fe3O4 content (47%) in spent catalyst, which is ascribed to the strong Fe oxide-SiO2 interaction hindering its deep reduction into metallic Fe but terminating as FeO. The reduced FeO could not be efficiently carburized into χ-Fe5C2 and tends to oxidize into Fe3O4 during the FTS reaction. Furthermore, the factors determining CO2 selectivity are systematically investigated based on abundant experiments. Results show that CO2 selectivity is closely related to CO conversion, Fe phase composition, reaction conditions, and the presence of K promoter. In brief, when the factor enhances H*/C* ratio on χ-Fe5C2, the reaction of dissociative O* from CO shifts towards hydrogenation to H2O despite that its reaction with CO* to form CO2via Boudouard mechanism is kinetically favorable. In addition, CO2 selectivity could be reduced via reverse water-gas shift (RWGS) reaction on Fe3O4 with H2O generation.

Highly stable Ru nanoparticles incorporated in mesoporous carbon catalysts for production of γ-valerolactone

The hydrogenation of levulinic acid to γ-valerolactone with water as solvent is a crucial reaction for producing fine chemicals. However, the development of highly stable catalysts is still a major challenge. Here, we prepared a Ru nanoparticles incorporated in mesoporous-carbon (Ru-MC) catalyst to achieve high stability in acidic aqueous medium. The Ru-MC showed excellent catalytic performance (12024 h−1 turnover frequency) in the hydrogenation of LA-to-GVL. Compared with Ru supported on mesoporous carbon catalyst (Ru/MC) prepared by conventional wet impregnation method, the Ru-MC showed excellent reusability (more than 6 times) and thermal stability (up to 600 °C). Based on H2-TPR-MS characterization, it was proposed that the incorporated structure significantly increased the interaction between Ru nanoparticles and carbon support, which effectively prevent the leaching and sintering of Ru nanoparticles and contributed to increased high reusability and thermal stability of the Ru-MC.

The Role of Surface Functionalities in PtGe and PtIn Catalysts for Direct Methanol Fuel Cells

Bimetallic PtGe and PtIn catalysts were prepared over Vulcan carbon (VC) and multiwall carbon nanotubes (NT) by conventional impregnation method (CI). These supports were functionalized with citric or nitric acid. The structural and electrochemical characteristics of the different functionalized supported catalysts were analyzed in order to determine the influence of the functional groups. The methods applied were temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), cyclohexane dehydrogenation reaction (CHD), and CO stripping. The functionalization treatment with citric or nitric acid eases CO oxidation to CO2, decreasing poisoning effect of CO over Pt, due to the development of oxygenated groups on support surfaces and in the nearby Ge and In. Bimetallic catalysts supported on carbons functionalized with HNO3 present increasing electrochemical active surface values, indicating a better electrochemical behavior than the corresponding monometallic catalysts. DMFC experiments show a very good behavior of PtGe catalysts, mainly for those supported on HNO3-functionalized NT, reaching a maximum power density of 80 mW cm−2. Conversely, PtIn catalysts exhibit a very poor behavior.