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1.
Hydrogen production via steam reforming of methanol is carried out over Cu/(Ce,Gd)O2−x catalysts at 210–600 °C. The CO content in reformate is about 1% at 210–270 °C, which are the typical temperature for hydrogen production via steam reforming of methanol. Largest H2 yield and CO2 selectivity and smallest CO content are obtained at 240 °C. The formation rate of CO increases with increasing temperature. The average formation rate of CO becomes larger than that of CO2 at about 450 °C. The H2 yield, the CO2 selectivity and the CO content become constant at about 550 °C. At 240 °C, the smallest CO content is obtained with a catalyst weight of 0.5 g and a Cu content of 3 wt%. The H2 yield, defined as H2/(CO + CO2) in formation rates, at 240 °C is always 3 and not affected by the variations of either the catalyst weight or the Cu content. 相似文献
2.
《International Journal of Hydrogen Energy》2020,45(53):28626-28639
Mesoporous xNi-yMg-Al2O3 catalysts prepared by combined evaporation induced self-assembly (EISA) and one-pot techniques were tested in CO2 methanation reaction. All calcined/reduced materials were characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), N2 physisorption, thermogravimetric analysis (TGA), CO2 adsorption, H2 temperature programmed reduction (H2-TPR) and transmission electron microscopy (TEM). The effects of Mg and Ni loadings on the catalysts properties and performances were systematically studied. Higher Mg contents enhanced methanation performances due to more favourable metallic interactions between the Ni, Mg and Al species. In addition, higher Ni contents led to better selectivity to CH4 by enhancing methane formation that involves H2 dissociation on Ni0 sites. The mesoporous 5Ni–Al2O3 catalyst obtained by the EISA-one-pot technique was significantly more active than silica-based catalysts with same 5 wt% Ni content supported on USY zeolite and SBA-15. Moreover, the performances of the most promising 15Ni–7Mg–Al2O3 mesoporous material were similar to those of a commercial 25Ni/γ-Al2O3 catalyst in spite of its reduced nickel content. 相似文献
3.
《International Journal of Hydrogen Energy》2021,46(77):38281-38298
Highly ordered mesoporous γ-Al2O3 particles and MgO materials were synthesized by evaporation induced self-assembly (EISA) and template-free hydrothermal co-precipitation routes, respectively. Ni, Ni–MgO, and Ni–La2O3-containing catalysts were prepared using a wet-impregnation method. The synthesized catalysts were characterized by N2 adsorption–desorption, XRD, SEM-EDS, DRIFTS, XPS, TGA-DTA, and Raman spectroscopy analysis. The mesoporous γ-Al2O3 catalyst support exhibited a high surface area of 245 m2/g and average pore volume of 0.481 cm3/g. The DRIFTS results indicate the existence of large Lewis's acid regions in the pure γ-Al2O3 and metal-containing catalysts. Catalytic activity tests of pure materials and metal-containing catalysts were carried out at the reaction temperature of 750 °C and a feed molar ratio of AA/H2O/Ar:1/2.5/2 over 3 h. Complete conversion of acetic acid and 81.75% hydrogen selectivity were obtained over the catalyst 5Ni@γ-Al2O3. The temperature and feed molar ratio had a noticeable impact on H2 selectivity and acetic acid conversion. Increasing the water proportion in the feed composition from 2.5 to 10 considerably improved the catalytic activity by increasing hydrogen selectivity from 81.75% to 91%. Although the Ni-based γ-Al2O3-supported catalysts exhibited higher activity performance compared to the Ni-based MgO-supported catalysts, they were not as resistant to coke formation as were MgO-supported catalysts. The introduction of MgO and La2O3 into the Ni@γ-Al2O3 and Ni@MgO catalysts' structures played a significant role in lowering the carbon formation (from 37.15% to 17.6%–12.44% and 12.17%, respectively) and improving the thermal stability of the catalysts by decreasing the agglomeration of acidic sites and reinforcing the adsorption of CO2 on the catalysts' surfaces. Therefore, coke deposition was reduced, and catalyst lifetime was improved. 相似文献
4.
《International Journal of Hydrogen Energy》2022,47(88):37218-37226
The valorization of cow manure (CM), as bio-waste, under a CO2 atmosphere could be an attractive strategy for tackling the environmental problems related to waste management and CO2 emission and producing valuable syngas. For this purpose, highly loaded Ni–Al2O3 catalysts with alkaline-earth metals (Mg and Sr) were synthesized and applied to the gasification of CM under CO2. The lowest yields of bio-oil (16.98 wt %) and coke (0.34 wt %) and the highest yield of syngas (55.09 wt %) were obtained from the catalytic decomposition of hydrocarbons when Sr was incorporated into Ni/Al2O3 (SN-AO). The highest selectivity for H2 (34.23 vol %) and CO (37.16 vol %) were obtained applying SN-AO followed by Mg-promoted Ni/Al2O3 (MN-AO) and Ni/Al2O3 (N-AO) catalysts. With increasing gasification temperature from 750 °C to 850 °C, the syngas yield (from 55.09 to 70.17 wt %) and H2 concentration (from 34.23 to 38.03 vol %) increased considerably because of the endothermic gasification process. The yield and selectivity of syngas (H2 and CO) increased under CO2 compared to those obtained under N2, indicating the high potential of CO2 for the thermal decomposition and dehydrogenation of the volatile matter. 相似文献
5.
《International Journal of Hydrogen Energy》2019,44(39):21913-21925
CO2 hydrogenation to methanol plays an increasingly important role in fields of chemical engineering, energy generation and H2/CO2 utilization, and the prohibitive costs result partially from the high operating pressures required for practical application. Thus, a hybrid catalyst/adsorbent consisting of Cu-ZnO-ZrO2 supported on hydrotalcite (named CZZ@HT) was synthesized, characterized and analyzed in this study with the intent that the adsorbent hydrotalcite would enhance the local concentration of CO2 and assist in catalyst dispersion. The as-prepared CZZ@HT catalyst containing 43.4 wt% of CuO-ZnO-ZrO2 in the form of well dispersed nanoparticles possessed a considerable BET surface area and external surface area after reduction. A remarkable copper dispersion of 58.7% was thereby achieved. This reduced catalyst displayed elevated uptakes of H2O and CO2 at 473 K compared to the reference adsorbent-free catalyst and presented enhanced adsorption capacities of CO2 at reaction temperatures due to collective effects of physisorption and chemisorption. Catalysis experiments on a fixed bed reactor using the rCZZ@HT catalyst showed a methanol selectivity of 83.4% and a SMeOH/SCO ratio of 5.0 in products. A control experiment in which hydrotalcite was replaced with quartz (named rCZZ&QS) showed considerably lower conversion at low pressure and demonstrated the enhancing effect of the hydrotalcite support. The new catalyst could achieve the same methanol productivity as the control catalyst at 2.45 MPa lower reaction pressure. This lower pressure corresponds to a ∼61.3% savings in energy consumption for compression. Accordingly, the CZZ@HT is a promising candidate for CO2 hydrogenation to methanol at moderate pressures. 相似文献
6.
《International Journal of Hydrogen Energy》2023,48(64):25006-25015
20 wt.% cobalt catalysts supported on pure and 5 wt.% silica-containing alumina have been prepared and characterized by X-Ray Diffraction, IR and DR-UV-vis-NIR spectroscopies and Field-Emission Scanning Electron Microscopy (FE-SEM). The presence of a cobalt-containing surface spinel phase Co3-xAlxO4 and, for the silica-containing sample, of a segregated Co3O4 phase is evident. These catalysts have been tested in CO2 hydrogenation at atmospheric pressure in steady state conditions in the temperature range 523–773 K. Both catalysts are active in CO2 hydrogenation to methane (methanation) and to CO (reverse Water Gas Shift, rWGS). CO2 hydrogenation activity is higher on freshly pre-reduced silica-free Co/Al2O3, while selectivity to methane is slightly higher on the silica-containing sample. Spent catalysts contain clustered or amorphous cobalt metal centers as active sites for methanation. The silica-containing catalyst shows slow deactivation in CO2 hydrogenation upon 13 h experiments, with quite stable or even slightly increasing rWGS activity and decreasing CH4 selectivity. This confirms previous data suggesting that, over cobalt catalysts, sites for methanation are metal centers prone to deactivation by carbon deposition. However, in contrast with what happens with unsupported and silica-supported cobalt catalysts, where deactivation is very fast, over these alumina-based catalysts carbon deposition and deactivation occur much more slowly. Sites for rWGS are unreduced cobalt centers which do not undergo such a deactivation phenomenon. 相似文献
7.
《International Journal of Hydrogen Energy》2020,45(46):24595-24603
Ce-promoted Ni/Al2O3 catalysts with Ce contents of 0, 5, 10, 15, and 20 wt% were investigated for CO2 methanation. Ni/15Ce/Al2O3 showed good selectivity and catalytic performance in CO2 methanation and remained stable at 350 °C for 80 h with minor fluctuations. Interactions between Ni and the Ce/Al2O3 support was characterized using X-ray diffraction, temperature-programmed reduction of H2, temperature-programmed desorption of CO2, X-ray photoelectron spectroscopy, Raman spectroscopy, and thermogravimetric analysis. Addition of Ce did not increase the catalytic surface area, which can significantly enhance the heterogeneous catalytic activity. However, XPS analysis showed that the Ce on the Ni/Al2O3 catalyst changed the surface electron states of Ni, Ce, and O. Additionally, CO2 adsorption/desorption was confirmed to be related to the amount of Ce present on Ni/Al2O3 by TGA and CO2-TPD. The Ce addition thus played an important role in determining the CO2 adsorption, desorption, and conversion. 相似文献
8.
《International Journal of Hydrogen Energy》2022,47(53):22442-22453
A series of supported Ni catalysts have been prepared from NixMg3?xAl hydrotalcite-like compounds (HTlcs) and the influence of Ni:Mg molar ratio on the structural property and catalytic activity for CO2 methanation is investigated. The catalysts were characterized by N2 physical adsorption, X-ray powder diffraction (XRD), temperature-programmed reduction (H2-TPR), temperature-programmed desorption (CO2-TPD), H2 chemisorption, scanning electronic microscopy (SEM), scanning transmission electronic microscopy (STEM), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). By reducing HTlcs at 800 °C, well dispersed Ni particles with average size of 5–10 nm are formed. The Ni crystal size decreases with the decrease of Ni:Mg ratio, attributable to the strong interaction between nickel and magnesium oxides. Among the catalysts, Ni2Mg1Al-HT shows the highest activity, giving ~93% CO2 conversion and >99% CH4 selectivity at 275 °C and SV = 5000 mL g?1 h?1. Meanwhile, this catalyst exhibits good stability without obvious sintering and coking. The high activity is related to the large amount of surface Ni0 species and medium basic sites. From CO2-TPD and DRIFTS, it is inferred that CO2 adsorbs on the medium basic sites, i.e., Ni–Mg(Al)O interface, forming monodentate carbonate. In situ DRIFTS reveals that monodentate carbonate, monodentate formate, and adsorbed CO are the main intermediate species, suggesting that the reaction may proceed via the formate formation route. 相似文献
9.
《International Journal of Hydrogen Energy》2023,48(7):2605-2616
A series of Cu@ZrO2-U framework catalysts derived from Cu@UiO-67 precursors with adjustable copper loadings were constructed by the deposition-precipitation method, and the catalytic activities of methanol synthesis via CO2 hydrogenation were investigated. The optimized 20-Cu@ZrO2-U catalyst showed the best catalytic activity. At 3 MPa and 260 °C, the space-time yield of CH3OH (STYCH3OH) reached 2.28 mmolCH3OH/(gcat·h), which was 3.5 times higher than that of 20-Cu/ZrO2. The catalyst of 20-Cu@ZrO2-U also showed good stability during the 100-h time on stream test. The catalysts were further characterized by XRD, N2 sorption, TEM, XPS, H2-TPR, CO2/H2-TPD and in situ DRIFTS. The characterization results showed that the stable ZrO2 framework derived from UiO-67 is propitious to the confine of copper nanoparticles and formation of Cu+-ZrO2 interfacial sites, which should be responsible for the excellent performance of methanol synthesis. Moreover, in situ DRIFTS was used to probe that the methanol synthesis via CO2 hydrogenation over 20-Cu@ZrO2-U follows a HCOO1-intermediated reaction pathway. 相似文献
10.
《International Journal of Hydrogen Energy》2018,43(49):22329-22339
Efficient catalysts with high selectivity in products are highly desirable for photocatalytic CO2 reduction. In this work, hydroxyapatite (HAP) decorated TiO2 (HAP/TiO2) were successfully fabricated via in-situ deposition of Ca(OH)2 on rutile TiO2 followed by a facile hydrothermal reaction. Comparing with TiO2, HAP/TiO2 exhibited significant enhancement (ca. 40 times) toward photocatalytic CO2 reduction in the presence of H2O with a >95% selectivity of CH4. The characterizations revealed HAP possessed Lewis basic sites (O2− in -PO43- groups) and Lewis acidic sites (Ca2+ or OH− vacancies), where Lewis basic sites could enhance the adsorption/activation of CO2 and Lewis acidic sites facilitated the adsorption/dissociation of H2O respectively, thus promoting the photocatalytic reduction and oxidation half-reactions of CO2 and H2O over Pt/TiO2. The formation of much more stable intermediates over HAP/TiO2 would be responsible for the high selectivity of CH4. Moreover, photoelectrochemical and electrochemical characterizations revealed HAP could also promote the charge separation of TiO2 and the charge transfer between TiO2 and adsorbed species. The findings demonstrate HAP has a great potential as efficient assistant for photocatalytic CO2 reduction with H2O and will stimulate us to design novel semiconductor-based materials with tuned Lewis acidic and Lewis basic sites to achieve highly efficient photocatalysts. 相似文献
11.
《能源学会志》2020,93(2):482-495
In this research, mesoporous high surface area Ni-Al2O3 catalysts promoted with different transition metals (Cr, Fe, Mn, Cu, and Co) were synthesized via ultrasound-assisted co-precipitation method and their performance was explored in CO2 methanation process. The promoters can affect the textural and catalytic properties of the Ni-Al2O3 catalysts to some extent. Powder X-ray diffraction (XRD), scanning electron microscopy (SEM), temperature programmed reduction with hydrogen (H2-TPR), and N2 adsorption-desorption (BET) were used for the characterization of the prepared samples. From the BET results, it was found that the incorporation of 5 wt% of the promoter into Ni-Al2O3 catalysts caused a decrease in the surface area, NiAl2O4 crystalline size and an increase in the mean pore diameter and total pore volume. Among the samples, the catalyst modified by Mn, exhibited the higher catalytic activity and selectivity towards CH4, especially at low temperatures (200–350 °C). These results could be explained by highest Ni active sites dispersion of this catalyst and enhancement of the catalyst reducibility at the low temperatures. The effect of Mn content was also evaluated and the results revealed that the Ni-Al2O3 sample modified with 3 wt% Mn with the highest BET surface area and the lowest crystalline size possessed the best catalytic performance. To further investigate the influence of ultrasonic irradiation, the optimal catalyst was prepared with a conventional co-precipitation method and its textural and catalytic properties were compared with those obtained for the catalyst prepared with the ultrasonic assisted coprecipitation method. Also, 25Ni-3Mn-Al2O3 catalyst showed a stable performance at 350 °C for 10 h in the CO2 methanation reaction. 相似文献
12.
The aim of this work is to study the influence of the addition of different oxides to an alumina support, on surface acidity and platinum reducibility in platinum-based catalysts, as well as their effect on the activity and selectivity in CO preferential oxidation, in presence of hydrogen. A correlation between surface acidity and acid strength of surface sites and metal reducibility was obtained, being Pt-support interaction a function of the acid sites concentration under a particular temperature range. In platinum supported on alumina catalysts, CO oxidation follows a Langmuir-Hinshelwood mechanism, where O2 and CO compete in the adsorption on the same type of active sites. It is noteworthy that the addition of La2O3 modifies the reaction mechanism. In this case, CO is not only adsorbed on the Pt active sites but also on La2O3, forming bridge bonded carbonates which leads to high reactivity at low temperatures. An increase on temperature produces CO desorption from Pt surface sites and favours oxygen adsorption producing CO2. CO oxidation with surface hydroxyl groups was activated producing simultaneously CO2 and H2. 相似文献
13.
《International Journal of Hydrogen Energy》2020,45(15):8418-8432
Three Ni/CeZrO2/MgAl2O4 catalysts synthesized using different Zr/Ce molar ratios (0.25, 1, and 4) were studied for methane tri-reforming. The catalysts were characterized using XRD, 27Al-NMR, H2-TPR, CO2-TPD, XPS, and in situ techniques (XPD and XANES). The addition of CeZrO2 at Zr/Ce = 0.25 on the MgAl2O4 spinel support considerably reduced the amount of carbon deposits, because the methane decomposition reaction was attenuated by the presence of less agglomerated Ni0 species produced after the reduction process. The highest CO2 adsorption capacity (basicity) was associated with the participation of medium-strength basic sites, which facilitated coke gasification and led to higher CO2 conversions. A syngas with quality (H2/CO ratio) of 1.8 was produced, suitable for use in Fischer-Tropsch reactions. 相似文献
14.
《International Journal of Hydrogen Energy》2019,44(29):14831-14841
A series of CuOZnOTiO2ZrO2 catalysts were prepared by a facile solid-state route, and the effects of adding citric acid or oxalic acid on the physicochemical properties and catalytic performance for CO2 hydrogenation to methanol were investigated. The catalysts were characterized by several techniques, including X-ray diffraction (XRD), N2 adsorption, transmission electron microscopy (TEM), reactive N2O adsorption, X-ray photoelectron spectroscopy (XPS), atomic absorption spectroscopy (AAS), temperature-programmed reduction with H2 (H2-TPR), and adsorption of CO2 followed by temperature programmed desorption (CO2-TPD). The results reveal that the addition of assistant complexing agents can improve the CuO dispersion in the catalysts and increase the metallic Cu surface area, and consequently greatly increase the CO2 conversion and methanol yield, with oxalic acid being a more effective assistant complexing agent than citric acid. 相似文献
15.
J.L. Contreras J. Salmones J.A. Colín-Luna L. Nuño B. Quintana I. Córdova B. Zeifert C. Tapia G.A. Fuentes 《International Journal of Hydrogen Energy》2014
This review aims to provide an overview of the main catalytic studies of H2 production by ethanol steam reforming (ESR). The reaction is endothermic and produces H2, CO2, CH4, CO and coke. The conversion and H2 selectivity of these products depended greatly of the physicochemical properties of the catalysts, active metal, promoters, temperature, long-term reaction, water/ethanol ratio, space velocity, contact time, and presence of O2. Initial total conversion has been reported in all catalysts evaluated between 300 and 850 °C. The noble catalysts with high selectivity to H2 (more than 80%) were: Rh, Ru, Pd and Ir and non-noble metal catalysts were: Ni, Co and Cu. The support materials include CeO2, ZnO, MgO, Al2O3, zeolites-Y, TiO2, SiO2, La2O2CO3, CeO2–ZrO2 and hydrotalcites. The impregnation method produced the best noble metal catalysts in terms of selectivity and conversion. The decrease of coke was related with the presence of basic sites on the support. 相似文献
16.
《International Journal of Hydrogen Energy》2022,47(48):20867-20880
Hydrogen purification by removing CO traces was studied via the preferential CO oxidation (PROX) reaction using highly dispersed Pt catalysts supported on dual oxide FeOx/TiO2. These catalysts were prepared by the strong electrostatic adsorption (SEA) method by varying the pH of synthesis and the calcination temperature. By measuring the point of zero charge (PZC) of the support components, it was possible to determine the pH in which Pt can be selectively deposited onto one of the support components, obtaining Pt dispersion values above 90%. The selective SEA of a Pt precursor onto the co-support (FeOx) was achieved at a synthesis pH between the PZCs of the support components (i.e., TiO2 PZC = 5.2 and Fe2O3 PZC = 6.9) by using a Pt anionic complex. The catalytic activity for the PROX reaction, expressed in terms of the CO conversion, O2 selectivity to CO2, apparent activation energy, and turnover frequency, confirmed that the SEA prepared catalysts were active and selective for the PROX reaction. XPS and TPR results of the Pt/FeOx/TiO2 catalysts showed the formation of Pt-FeOx interfaces, called as (Pt-FeOx)i interfacial sites, which enhanced the stability and catalytic activity for the PROX reaction. The concentration of these sites can be controlled by the synthesis conditions used, mainly pH and to a lower extent the calcination temperature. 相似文献
17.
《International Journal of Hydrogen Energy》2023,48(55):21224-21239
The self-regeneration of Ni-based catalysts has been considered as a promising approach to maintain not only a continuous but also economical process. However, the effect of catalyst nature, operating temperature, amount and types of carbon deposits on the effectiveness of the in-situ regeneration is still not well-investigated. Therefore, in this work, the self-regeneration ability of the undoped and Dy-doped Ni/SiO2 catalysts, which were prepared by the same impregnation method, were examined in the dry reforming of methanol. The physicochemical properties of the fresh and spent catalysts were analyzed by various techniques such as X-ray diffraction (XRD), hydrogen temperature-programmed reduction (H2-TPR), oxygen temperature-programmed desorption (O2-TPD), transmission electron microscopy (TEM), N2-BET isothermal adsorption. The nature and chemical reactivity of coke deposits formed during dry reforming at various temperatures (550, 600, and 650 °C) and the regeneration possibility of used catalysts through CO2 gasification at these temperatures were investigated by the in-situ temperature-programmed gasification by CO2 (TPCO2). The Dy additive significantly improves the dispersion of the nickel active sites of Ni/SiO2 catalyst, as demonstrated by the decreased Ni crystal size as well as the increased specific surface area and reduction degree of the catalyst. Furthermore, Dy promotion increases the quantity of oxygen vacancies and the nature of oxygen species, thereby improving the catalyst activity and stability. Specifically, methanol conversion dropped from 93% to 96%–61% and 31% for undoped Ni/SiO2 at 600 °C and 650 °C, respectively and from about 99% to 87% (at 600 °C) and 52% (at 650 °C) for Dy-doped catalyst. 相似文献
18.
《International Journal of Hydrogen Energy》2021,46(65):32809-32845
Today, bi - reforming of methane is considered as an emerging replacement for the generation of high-grade synthesis gas (H2:CO = 2.0), and also as an encouraging renewable energy substitute for fossil fuel resources. For achieving high conversion levels of CH4, H2O, and CO2 in this process, appropriate operation variables such as pressure, temperature and molar feed constitution are prerequisites for the high yield of synthesis gas. One of the biggest stumbling blocks for the methane reforming reaction is the sudden deactivation of catalysts, which is attributed to the sintering and coke formation on active sites. Consequently, it is worthwhile to choose promising catalysts that demonstrate excellent stability, high activity and selectivity during the production of syngas. This review describes the characterisation and synthesis of various catalysts used in the bi-reforming process, such as Ni-based catalysts with MgO, MgO–Al2O3, ZrO2, CeO2, SiO2 as catalytic supports. In summary, the addition of a Ni/SBA-15 catalyst showed greater catalytic reactivity than nickel celites; however, both samples deactivated strongly on stream. Ce-promoted catalysts were more found to more favourable than Ni/MgAl2O4 catalyst alone in the bi-reforming reaction due to their inherent capability of removing amorphous coke from the catalyst surface. Also, Lanthanum promoted catalysts exhibited greater nickel dispersion than Ni/MgAl2O4 catalyst due to enhanced interaction between the metal and support. Furthermore, La2O3 addition was found to improve the selectivity, activity, sintering and coking resistance of Ni implanted within SiO2. Non-noble metal-based carbide catalysts were considered to be active and stable catalysts for bi-reforming reactions. Interestingly, a five-fold increase in the coking resistance of the nickel catalyst with Al2O3 support was observed with incorporation of Cr, La2O3 and Ba for a continuous reaction time of 140 h. Bi-reforming for 200 h with Ni-γAl2O3 catalyst promoted 98.3% conversion of CH4 and CO2 conversion of around 82.4%. Addition of MgO to the Ni catalyst formed stable MgAl2O4 spinel phase at high temperatures and was quite effective in preventing coke formation due to enhancement in the basicity on the surface of catalyst. Additionally, the distribution of perovskite oxides over 20 wt % silicon carbide-modified with aluminium oxide supports promoted catalytic activity. NdCOO3 catalysts were found to be promising candidates for longer bi-reforming operations. 相似文献
19.
《International Journal of Hydrogen Energy》2022,47(61):25471-25485
Steam reforming of liquid hydrocarbon fuels is an appealing way for the production of hydrogen. In this work, the Rh/Al2O3 catalysts with nanorod (NR), nanofiber (NF) and sponge-shaped (SP) alumina supports were successfully designed for the steam reforming of n-dodecane as a surrogate compound for diesel/jet fuels. The catalysts before and after reaction were well characterized by using ICP, XRD, N2 adsorption, TEM, HAADF-STEM, H2-TPR, CO chemisorption, NH3-TPD, CO2-TPD, XPS, Al27 NMR and TG. The results confirmed that the dispersion and surface structure of Rh species is quite dependent on the enclosed various morphologies. Rh/Al2O3-NR possesses highly dispersed, uniform and accessible Rh particles with the highest percentage of surface electron deficient Rh0 active species, which due to the unique properties of Al2O3 nanorod including high crystallinity, relatively large alumina particle size, thermal stability, and large pore volume and size. As a consequent, Rh/Al2O3-NR catalyst exhibited superior catalytic activity towards steam reforming reactions and hydrogen production rate over other two catalysts. Especially, Rh/Al2O3-NR catalyst showed the highest hydrogen production rate of 87,600 mmol gfuel?1 gRh?1min?1 among any Rh-based catalysts and other noble metal-based catalysts to date. After long-term reaction, a significant deactivation occurred on Rh/Al2O3–NF and Rh/Al2O3-SP catalysts, due to aggregation and sintering of Rh metal particles, coke deposition and poor hydrothermal stability of nanofibrous structure. In contrast, the Rh/Al2O3-NR catalyst shows excellent reforming stability with negligible coke formation. No significantly sintering and aggregation of the Rh particles is observed after long-term reaction. Such great catalyst stability can be explained by the role of hydrothermal stable nanorod alumina support, which not only provides a unique environment for the stabilization of uniform and small-size Rh particles but also affords strong surface basic sites. 相似文献
20.
《International Journal of Hydrogen Energy》2023,48(64):25031-25043
The catalytic performance in the direct CO2 methanation of a model biogas is investigated on NiO–CeO2 nanostructured mixed oxides synthesized by the soft-template procedure with different Ni/Ce molar ratios. The samples are thoroughly characterized by means of ICP-AES, XRD, TEM and HR-TEM, N2 physisorption at −196 °C, and H2-TPR. They result to be constituted of CeO2 rounded nanocrystals and of polycrystalline needle-like NiO particles. After a H2-treatment at 400 °C for 1 h, the surface basic properties and the metal surface area are also assessed using CO2 adsorption microcalorimetry and H2-pulse chemisorption measurements, respectively. At increasing Ni content the Ni0 surface area increases, while the opposite occurs for the number of basic sites. Using a CO2/CH4/H2 feed, at 11,000 cm3 h−1 gcat−1, CO2 conversions in the 83–89 mol% range and methane selectivities >99.5 mol% are reached at 275 °C and atmospheric pressure, highlighting the very good performances of the investigated catalysts. 相似文献