Search

We report a physical mixture of 1 wt% Ru/Al 2 O 3 with 10 wt% Ni/Al 2 O 3 obtained from the NiAl 2 O 4 phase as a highly active, durable, and cost-effective catalyst for the dry reforming of methane (DRM). Since the presence of Ru facilitates the reduction of Ni oxides, resulting in not only enhanced CH 4 conversion but also increased carbon deposits, the optimal formation of metallic Ni sites is a key factor for the mixed Ru-Ni catalyst. Here, we used a NiAl 2 O 4 /Al 2 O 3 catalyst and reduced it with CH 4 under reaction conditions for the limited formation of metallic Ni sites, depending on the reaction temperatures. As a result, this mixed catalyst showed higher performance for DRM than a Ru single catalyst with mild carbon deposits at both low (650 ℃) and high (800 ℃) temperatures taking advantage of improved cost-effectiveness, on top of that, the existence of a Ni catalyst compensated for the loss of activity of a Ru catalyst due to sintering. We also suggest different mechanisms for DRM over the Ru catalyst and Ni catalyst respectively from the results of temperature-programmed surface reaction and CH 4 /CO 2 cycling experiments. [Display omitted] • The presence of Ru facilitates the reduction of Ni oxides. • The optimal formation of metallic Ni sites is a key factor for the Ru-Ni catalyst. • A physical mixture of RuO 2 /Al 2 O 3 with NiAl 2 O 4 /Al 2 O 3 shows the best activity for DRM. [ABSTRACT FROM AUTHOR]

Alumina oxide supported nickel (Ni/Al2O3) catalysts generally suffer from fast deactivation caused by coking and formation of nickel aluminate (NiAl2O4) in dry reforming of methane (DRM). Herein, for the first time, a self-stabilization mechanism of the Ni/Al2O3 catalyst (with 0.1 wt% Ni loading) was revealed and effectively applied for DRM. Namely, the conversion of catalytically active Ni species into catalytically inert NiAl2O4 spinel in DRM over the Ni/γ-Al2O3 catalyst could be mitigated by repeated reduction-reaction treatments owing to the increasing amount of Ni located on the NiAl2O4 isolation layer rather than the reactive γ-Al2O3. The self-stabilization could be achieved over Ni/α-Al2O3 as well, even with a faster rate, since the NiAl2O4 isolation layer can be directly formed in the first reduction-reaction cycle due to its small surface area and weak metal-support interaction. These observations not only highlight the importance of an isolation layer for protecting the catalyst from deactivation, but also provide a novel and efficient self-stabilization approach for catalytic DRM. [ABSTRACT FROM AUTHOR]

[Display omitted] • 1. Proposed the "Ni-NiO synergistic effect" to achieve optimal activity and stability in CO methanation reaction. • 2. Synergistic effect of Ni and NiO reduces the overall reaction system energy barrier. • 3. Hydrogen reduction regulates the dimensions and valence states of Ni species in Ni/Al catalysts. The synthesis of methane from syngas represents a pivotal technology in the artificial synthesis of natural gas, with the study of methanation catalysts being a fundamental aspect of this process. Extensive research has focused on CO methanation using Ni/Al 2 O 3 catalysts; however, enhancements in catalyst stability and low-temperature activity are still required. This research investigated the structure of Ni/Al 2 O 3 under H 2 reduction at varying temperatures and the catalytic performance in natural gas synthesis (SNG) through CO methanation. It was observed that a higher reduction temperature resulted in nickel species agglomeration. Notably, Ni catalysts reduced at 600 °C demonstrated optimal CO conversion and CH 4 selectivity under the tested conditions. Characterization studies uncovered a synergistic effect between Ni and NiO species, which was most effective for catalytic activity under hydrogen reduction at 600 °C but only at an appropriate reduction temperature. These insights are significant for the advancement of Ni/Al 2 O 3 methanation catalysts in natural gas production. [ABSTRACT FROM AUTHOR]

[Display omitted] • A mechanism for sulfur poisoning the Ni/Al 2 O 3 catalyst was proposed. • The main factor accelerating catalyst poisoning is the migration of elemental S. • The catalyst adding 1.0% SiO 2 exhibits improved sulfur tolerance. • Smaller Ni particles are more sulfur-tolerant than larger ones. Dry reforming of methane (DRM) is the method to convert two greenhouse gases to synthesis gas. The nickel-based catalysts used in the DRM are extremely easily poisoned by H 2 S in the feed gas, however, the associated poisoning process is not clear. In this work, a mechanism for poisoning the Ni/Al 2 O 3 catalyst by elemental sulfur migration was proposed, and silica was added to the catalyst to prolong the sulfur tolerance of the catalyst. From the characterizations of the catalyst with different methods, it was noted that the main factor accelerating catalyst poisoning was the formation and migration of elemental sulfur. The catalyst Ni/Al 2 O 3 with 1.0 % SiO 2 exhibited improved sulfur tolerance. The addition of SiO 2 inhibits the growth of Ni particles during the reduction process, and the smaller Ni particles lead to less coke and a longer period of sulfur tolerance. [ABSTRACT FROM AUTHOR]

In this work, the performance of a series of nickel catalysts supported on alumina containing the promoters Mg, Mn, Ce and P was evaluated against the dry reforming of methane (DRM). Alumina support was obtained quickly and simply through the microwave-assisted combustion method using low levels of urea. The catalysts were characterized by XRD, TPR, FTIR and XRD in situ , proving that successive hydration and heat treatment steps during synthesis can generate modifications in the alumina phases, in addition to the formation of aluminate species that are reduced during the catalytic activation step and modify the level of interaction between active and support phases. The catalytic activity test was performed with GHSV = 100 L g−1 h−1 and the formed carbon was quantified by thermogravimetric analysis. The Mn promoter exhibited the highest methane conversion rate during the initial stages of the reaction, in which the presence of MnO 2 favored parallel reactions of methane decomposition. The phosphorus and cerium produced smaller amounts of coke, reducing the carbon generated due to the interaction of promoters with carbon on the surface of the catalytic sites. The Mg increases the interaction of the active phase with the support. [Display omitted] • Microwave-assisted selfcombustion with low fuel content was efficient in synthesis of alumina in a quick one-step method. • Sequential wet-impregnation steps and thermal treatment change the crystalline structure of support Al 2 O 3. • Phosphorus presence as promoter decrease the reduction temperature of active phase and produced H 2 /CO ratio nearly one. • The manganese promoter increase the conversion rate of CH 4 and CO 2 in catalytic test. • Cerium insertion improved catalytic stability over 20h in GHSV = 100 L/g.h. [ABSTRACT FROM AUTHOR]

The precursors of Ni/Al2O3 catalysts with different metal contents (2–10 wt % Ni) and calcination temperatures were obtained by wet impregnation. Their composition and physicochemical properties were determined by low-temperature nitrogen adsorption, atomic absorption spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy (XPS), and temperature-programmed reduction (TPR) with hydrogen. The formation of free and chemically bound forms of nickel was studied by TPR-H2. Calcination above 400°C leads to complete binding of nickel with Al2O3, forming nickel–aluminum spinel. According to TPR-H2, free NiO appears in the samples calcinated at 550°C only at 10% Ni. The stability of the reduced catalysts to oxidation in air and the effect of the temperature of treatment with hydrogen on the reduction of the nickel forms bonded with the support were determined. The XPS and TPR studies showed that the oxidation of reduced nickel in air led to a transition from Ni2+ forms tightly bound with support to weakly bound forms that are more easily reduced. The catalytic action in hydrodechlorination of chlorobenzene (CB HDC) of the samples that differed in the ratio of weakly and tightly bound Ni forms was considered. The spinel forms that are nearly inactive in chlorobenzene hydrodechlorination can be reduced with hydrogen to form more active Ni0 sites under the reaction conditions. The active sites obtained by the reduction of Ni2+ forms weakly bound to the support are stable under chlorobenzene hydrodechlorination conditions. [ABSTRACT FROM AUTHOR]

Performance of Ni/Al2O3 catalysts (10 wt.% Ni) in steam reforming of n-butane was investigated in terms of n-butane conversion, selectivity to hydrogen and hydrogen yield. The process was carried out in a fixed-bed tubular reactor at 650 °C and atmospheric pressure. The volumetric flow rates of n-butane and steam were 0.1 mL/min and 0.6 mL/min, respectively. The catalysts were prepared by precipitation-sedimentation method at different precipitation, drying and calcination temperatures as well as precursor types. Synthesized catalysts were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and BET analyses. It was found that Ni- Nitrate as the precursor was more favorable than the other. Mathematical predictive formulas were generated for responses by Design Expert software. Also, the optimum condition of the catalyst preparation was obtained by using the response surface methodology (RSM). Ultimately, it was concluded that the overall optimum condition were: Tprecipitation= 30°C, Tdrying= 115°C, Tcalcination= 700°C .

Steam reforming of commercially available LPG using Ru/Al2O3and Ni/Al2O3catalysts has been studied at temperatures between 573 and 773 K. Ru/Al2O3catalyst showed higher rates of reaction and lower activation energies of the three main components of LPG, compared with Ni/Al2O3. However, Ni/Al2O3catalyst showed a better H2:CH4selectivity. The activation energy of n-butane was the lowest over Ru/Al2O3, whereas over Ni/Al2O3, propane had the lowest activation energy. The activation energy of i-butane was always the highest over both catalysts, which suggests that both catalysts performed better with unbranched molecules. A slight increase in activation energy was observed, when each component of the LPG mixture was studied separately as a pure gas, compared with being mixed in LPG. At a constant temperature of 773 K, hydrogen production yield and H2:CH4selectivity were determined using Ru/Al2O3at different steam:carbon (S:C) ratios and LPG flow rates. It was found that the yield and selectivity increased with the increase in S:C ratio and the decrease in the flow rate. The highest yield of 0.64 was achieved using S:C ratio of 6.5 and a LPG flow rate of 50 mL min−1. The work provides valuable information on steam reforming of pure components of LPG, compared with when they are in the mixture. The comparison is done using conventional steam reforming catalyst, Ni/Al2O3, and compared with Ru/Al2O3. The observed trends and variations in reaction rates, in pure and mixed gases, indicated that the mechanism of steam reforming of a hydrocarbon mixture depends on its composition. [ABSTRACT FROM AUTHOR]

• The performance of Y promoted Ni/Al 2 O 3 catalysts was investigated in SRM process. • Ni loading, Y loading, and support structure in SRM reaction were assessed. • 20Ni-3.0Y/HAl exhibited the best activity and stability in the SRM process. • 20Ni-3.0Y/HAl showed the minimum decreased conversion over 12 h SRM reaction. • Y improved the BET surface area of Ni/Al 2 O 3 catalysts. This work deals with the application of Y-promoted Ni-based catalysts supported on both bulk and hollow Al 2 O 3 supports with spherical shape in the steam reforming of methane (SRM) process. For evaluating the influence of Ni and Y loadings, 15, 20, and 25 wt% Ni and 1.5, 3.0, and 4.5 wt% Y were loaded on both alumina supports. Furthermore, for enhancing the stability and activity of SRM Ni-based catalysts, reaction temperature (600, 650, and 700 °C) and steam to methane (S/M) molar ratio (1.5 to 3.0) are also adjusted in this research. Various characterizing techniques listed as X-ray powder diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), transmission electron microscope (TEM), N 2 adsorption/desorption, energy dispersive X-ray spectroscopy (EDX), field emission scanning electron microscopy (FESEM), H 2 temperature programmed reduction (H 2 -TPR), and temperature programmed oxidation (TPO) were employed on the fresh and used catalyst. Improvements in metal dispersion, catalytic performance, and long-time stability in SRM were achieved with the aim of a hollow Ni-Y-Al catalyst. As a result, 20Ni-3.0Y/HAl depicted the highest methane conversion of 95.77 %, hydrogen yield of 97.74 %, and H 2 /CO molar ratio of 6.61 at 700 °C, which is probably due to the higher surface area of hollow alumina support in comparison with bulk one. [ABSTRACT FROM AUTHOR]

An impregnation-reduction method has been developed in this study to prepare the Ni/Al2O3 catalyst for steam reforming of bio-oil model compounds for hydrogen production. This method can alleviate the interactions between nickel species and an alumina carrier and promote metal dispersion and utilization of the nickel species, achieving a highly active, selective and stable reforming catalyst. Moreover, this method is very simple and fast. Only the impregnation and reduction steps are involved and the catalyst can be prepared in situ. In addition, coke formation in steam reforming is not uniform on a catalyst bed. Coking in the topmost catalyst layer is much more serious. [ABSTRACT FROM AUTHOR]

Highlights: [•] Ethanol–phenol mixture is steam reformed over Ni-Al2O3 at 800–900K. [•] Magnesium oxide increases activity but decreases sulphur resistance. [•] MgO modifies alumina activity inducing bigger Ni particles formation. [•] Addition of boron decreases activity with poor effect on S resistance. [Copyright &y& Elsevier]

Abstract: Ni/xPr-Al2O3 (x = 5, 10, 15, 20 wt%) catalysts with an application in autothermal reforming of methane were prepared by sequential impregnation synthesis; its catalytic performance was evaluated and compared with that of Ni/γ-Al2O3 catalyst; the physicochemical properties of the catalysts were characterized by X-ray diffraction (XRD), Transmission electron microscope (TEM), X-Ray Photoelectron Spectrometer (XPS), Thermo Gravimetric Analyzer (TGA) and H2-temperature programmed reduction techniques (TPR). The results showed that Pr addition promoted the reduction of nickel particle size on the surface. TPR experiments suggested a heterogeneous distribution of nickel oxide particles over xPr-Al2O3 supports and the promotion of NiO reduction by Pr modification. The CH4 conversion increased with elevating levels of Pr addition from 5% to 10%, then decreased with Pr content from 10% to 20%. For the stability catalytic tests, Ni/xPr-Al2O3 catalysts maintained the high activity after 48 h while Ni/Al2O3 had a significant deactivation. [Copyright &y& Elsevier]

Abstract: Catalyst deactivation during steam reforming of transportation fuels, primarily due to sulfur poisoning and carbon deposition, is a major hurdle in the commercialization of fuel cell technologies. In an attempt to better understand the phenomena, a previously formulated multi-component (Ni, Pd, Rh) catalyst supported on γ-Al2O3 was studied under steam reforming of Jet A spiked with thiophene to achieve a total sulfur content of 1000ppm by weight. Analysis of fresh catalysts showed the presence of two groups of active metal particles, primarily distinguished by their size and composition; small particles (1–5nm) largely comprised of Rh and large particles (10–20nm) that were predominantly Ni, with or without the presence of Pd. Analysis of used catalysts showed sintering of crystallites containing Ni but no identifiable growth in Rh crystallites. When complete conversion of sulfur compounds to hydrogen sulfide was observed, catalyst deactivation was minimized. However, when the conversion of sulfur compounds was low, significant catalyst deactivation was noted. In the presence of sulfur, increased amounts of cracking products were observed, suggesting that sulfur primarily affected the active sites responsible for steam reforming. Sulfur was preferentially adsorbed on the surface of Ni crystallites. It has been postulated that sulfur adsorption on Ni sites causes the initial deactivation of the catalyst which suppresses carbon gasification on the active sites, leading to the accumulation of carbon deposits over time. [Copyright &y& Elsevier]

Abstract: The reaction of acetic acid steam reforming for H2 production has been investigated over transition metal catalysts (Ni, Co, Fe or Cu)/Al2O3. Ni/Al2O3 and Co/Al2O3 catalysts are active for acetic acid steam reforming while Fe/Al2O3 and Cu/Al2O3 catalysts present negligible activity. The difference can be attributed to the different cracking activity of the metals toward the C–C and C–H bonds of acetic acid molecule. Detailed comparisons in terms of catalytic activity, selectivity, and stability are carried out over Ni/Al2O3 and Co/Al2O3 catalysts. Distinct product distributions were observed between them. CH4 production was favored over Ni/Al2O3 catalyst at mild temperatures while CO production was favored over Co/Al2O3 catalyst at high temperatures, which were induced by the different reaction networks over the two catalysts. Moreover, in the stability tests, Ni/Al2O3 catalyst was much more stable than Co/Al2O3 catalyst. Serious coke deposition and oxidation of metallic phase led to the fast deactivation of Co/Al2O3 catalyst. On the contrary, much slower coke formation rates and metal sintering rates as well as much higher resistivity of active metal toward oxidation guaranteed the stability of Ni/Al2O3 catalyst. [ABSTRACT FROM AUTHOR]

Abstract: Deactivation by sulfur poisoning and carbon deposition of steam reforming catalyst used for hydrogen production from diesel or jet fuel creates a significant barrier to commercialization of fuel cell technologies. Steam reforming of n-hexadecane on a rhodium/nickel catalyst supported on γ-alumina, a formulation previously proposed for steam reforming of logistic fuel, was used to study the deactivation mechanisms. The steam reforming activity was measured in terms of H2 yields and showed that the catalysts were stable in the absence of sulfur but deactivated over a period of 10h when sulfur was present at high loading. Stability and activity were higher with higher amounts of Rh content when Ni was kept constant. TEM-EDS of used catalysts revealed preferential adsorption of sulfur on the surface of Ni crystallites; EDS and XRD analysis showed no bulk sulfide formation. Excessive carbon deposition was observed during steam reforming of sulfur-containing fuel. Blocking of reactant species on the surface of the catalyst due to the formation of aromatic/polymeric carbon on the support was also seen, although higher Rh content inhibited this phenomenon. [Copyright &y& Elsevier]

[Display omitted] • Doping 3%Ni/Al 2 O 3 with 0.3 wt% In reduced coking in methane dry reforming. • 8 wt% CeO 2 over 3%Ni/Al 2 O 3 was less effective against coke deposition. • The co-promotion resulted almost no coking during 6 h DRM reaction at 650 °C. • Strong metal-support interaction provided Ni particles below 7 nm in all catalysts. • Interaction of NiIn particles with In-doped CeO 2 was proven. Herein, the promotion effect of only 0.3 wt% indium on 3% Ni/Al 2 O 3 and 3% Ni/CeO 2 -Al 2 O 3 catalysts prepared by deposition-precipitation over a commercial alumina and on the CeO 2 -modified support was studied. Catalyst characterization by XRD, TPR, XPS, TEM, CO-DRIFTS was performed. The catalytic properties were investigated and coke formation was analyzed under temperature ramped CH 4 -decomposition and in Dry Reforming of Methane (DRM). The unique impact of indium was compared to the well-known effects of ceria additive. The carbon deposition on Ni/Al 2 O 3 blocking the reactor could be only delayed due to ceria on Ni/CeO 2 -Al 2 O 3 , while NiIn/Al 2 O 3 was able to maintain the activity in DRM. Indium modifier acting in parallel with ceria over NiIn/CeO 2 -Al 2 O 3 determined the least coking, but the least catalytic activity. The results were discussed in terms of double role of In, acting as a ceria modifier, upgrading its oxidative properties and as a metal modifier, getting alloyed with Ni. [ABSTRACT FROM AUTHOR]

Bioleaching studies were carried out on a commercial nickel-based reforming catalyst using two acidophilic bacteria (Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans) under several types of bioleaching mode (one-step, two-step and spent medium-step) and catalyst pretreatment (with and without reduction). The highest percentage of nickel extraction was achieved using A. thiooxidans under spent medium-step (94.4 ± 0.1%). The percentage of nickel extracted was constant (85.6 ± 3.9%) up to a pulp density of 5% w v−1, and it decreased at higher pulp densities due to acid depletion. In order to assess the potential reuse of the recovered metal, the nickel solution obtained by bioleaching was recycled by using it to prepare a new Ni/Al 2 O 3 catalyst by impregnation of a commercial alumina support. Characterization of the catalyst prepared from recycled nickel showed that it had a high purity along with a suitable texture and metallic dispersion. Indeed, the activity of the new catalyst in the dry reforming of methane provided a high conversion of methane (99%) with good stability over time under the experimental conditions employed. Unlabelled Image • The highest Ni extraction was achieved by A. thiooxidans under spent medium-step mode. • The Ni extraction was constant (60.9 ± 2.7%) up to a pulp density of 5% w v−1. • An efficient DRM catalyst has been synthesized with Ni recovered by bioleaching. [ABSTRACT FROM AUTHOR]