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Steam reforming (SR) is a process for converting transportation fuels into hydrogen-rich gas, which can be fed to SOFCs for on-board power supplies. Herein, we prepare Mg x Ni 1-x O (0.5
The lack of detailed functions of different REMs in NH 3 decomposition to H 2 makes the efficient modified catalysts not rationally be designed though many REMs-modified catalysts have been reported. In this work, the 10Ni/A 1 Mg 4 O α (A = La, Ce, and Y) and 10Ni/MgO, in which supports were synthesized by the sol–gel method and Ni was loaded by the wet-impregnate method, were comparatively investigated to reveal the effect of REMs against NH 3 decomposition reaction. The presence of REMs enhanced the activity of 10Ni/A 1 Mg 4 O α and decreased the activation energy as greatly as by half compared to 10Ni/MgO. The produced H 2 in situ has little impact on the activity of 10Ni/A 1 Mg 4 O α , among which Ce has the most excellent H 2 desorption ability. The intrinsic activity of catalysts was improved better by Ce and Y than La and the best Ni particle size is around 6 nm according to TOF, though the Ni particle is the smallest (4.9 nm) in 10Ni/La 1 Mg 4 O α . The surface structure of catalysts was tuned by doping REMs, forming a solid solution and some defects (oxygen vacancies), which enhanced the interaction between active metal and support with obvious electron transfer from support to Ni obtaining a better Ni dispersion and making NiO easier to be reduced. Additionally, the catalysts doped by La or Ce possess more oxygen vacancy due to the changes of La 2 O 2 CO 3 and the valence of Ce, exhibiting stronger basic sites and better N 2 desorption capacity. The study offers a promising strategy for utilizing appropriate or multiple REMs to synthesize effective catalysts effectively for catalyzing NH 3 decomposition in the future.
Selective production of cyclohexanol from renewable lignin derived phenolic has been presented using the cost-efficient catalyst Ni/MgO which shows excellent catalytic activity in the hydrogenation reaction and dehydroxylation inhibition. Guaiacol, one of the most abundant lignin depolymerization products, was selected as the model compound. The hydrogenation performance of guaiacol was investigated over various catalysts. The effect of the reaction parameters was also studied. The results showed that guaiacol could be efficiently converted to cyclohexanol, which is a highly value-added precursor and additive for bio-fuel that is generally obtained from unsustainable fossil resources. Under the mild condition (160 °C, 3 h and 3 MPa H 2 ), more than 97.74% of guaiacol conversion with 100% cyclohexanol selectivity can be achieved in the presence of 20% Ni/MgO. Intensive catalyst characterization demonstrated that the efficient promotion effect of the base carrier for the Ni active center was responsible for efficient guaiacol conversion and selective cyclohexanol production. Furthermore, the Ni/MgO catalyst showed excellent recyclability, where no significant activity loss was observed even after four runs. Moreover, the reaction pathway and the catalytic mechanism are proposed.
The composite catalysts AC-Ni/MgO-Al 2 O 3 were prepared by the co-precipitation method with activated carbon (AC) and [Ni,Mg,Al]-hydrotalcite as the precursors, and characterized by XRD , TG-DTG, N 2 adsorption, H 2 -TPR and SEM, respectively. The resultant catalysts were examined for CO 2 reforming of methane. The results showed that the introduction of AC into Ni/MgO-Al 2 O 3 catalyst improved the textural properties, especially the surface area and pore volume of mesopores , and decreased the size of metal Ni. Compared with Ni/MgO-Al 2 O 3 , the composite AC-Ni/MgO-Al 2 O 3 exhibited higher catalytic activity , stability and H 2 /CO ratio. But the AC content obviously influenced the catalytic performances. High AC loading resulted in the decline of catalytic activity owing to lower surface area and fewer active Ni content in the catalyst. 10AC-Ni/MgO-Al 2 O 3 with 10% AC displayed the best catalytic activity and stability compared with Ni/MgO-Al 2 O 3 . About 86.2% conversion of CH 4 , 91.3% conversion of CO 2 and above 0.95 ratio of H 2 /CO were achieved over 10AC-Ni/MgO-Al 2 O 3 sample for the reaction time of 5430 min. This work provides a route to improve catalytic performances of Ni-based catalysts in CO 2 reforming of methane.
This work demonstrates the upgrading of lignin-derived monomers through a cascade demethoxylation, aqueous-phase reforming reaction, eliminating the need for external hydrogen supply. The core of this research lies in the use of neat water as both reaction medium and the hydrogen donor over a multifunctional Ni/MgO catalyst, which is responsible for water splitting, aqueous-phase reforming of in situ generated methanol, and selective cleavage of the C–O bond, finally establishing an efficient one-pot approach achieving a high yield of phenols. Reaction mechanism studies proved that the initial H* source came from water by its splitting on the surface of the Ni/MgO catalyst, which triggered the fracture of the aromatic ether bond to afford phenols and CH3O*. The subsequent aqueous-phase reforming of CH3O* and OH* generated more hydrogen and further accelerated the hydrodeoxygenation (HDO) process. A high conversion of 87.8% with a selectivity of 88.9% for phenol could be achieved at 190 °C from guaiacol. Thanks to the interesting water-splitting mechanisms and strong metal–support interaction (SMSI), Ni/MgO exhibited significantly enhanced stability compared to the previously reported nanoporous Ni catalysts. Further, with real lignin as the substrate, 16.3 wt % combined yield of phenol and 4-methylphenol could be acquired under optimized conditions. Overall, this “H2-free” approach offers a promising alternative to conventional biorefinery processes, addressing the challenges of hydrogen sourcing and economic feasibility.
To develop an efficient and feasible catalyst for converting inedible vegetable oil to green biodiesel via a one-step decarboxylation process, a series of Ni-based MgO-Al 2 O 3 catalysts with different active Ni species were fabricated by adjusting the various Ni loading amounts (2.5–20%) and applied to the catalytic deoxygenation of OA to generate green biodiesel. Additionally, the structure-property relationship, deactivation mechanism and regeneration performance were also evaluated via various characterization technologies (XRD, BET, NH 3 -TPD, H 2 -TPR, XPS, SEM-EDX, HRTEM, TGA, Raman as well as GC/MS and UV-fluorescence spectra). The experimental results indicated that Ni introduction obviously enhanced the conversion ratio. Ni (10%)/MgO-Al 2 O 3 catalysts exhibited excellent catalytic performance with the highest HCs (95.12%), olefin content (57.37%) and green biodiesel content (75.90%) due to mild Brønsted-rich acidity sites, lower reduction temperature, higher active metallic Ni species content, suitable oxygen vacancy content and favorable texture properties via the decarbonylation reaction pathway. Furthermore, lower Ni loading was beneficial to gasoline and bioaviation fuel generation due to higher Brønsted-rich acidity sites and total acid amount, which boosted C-C scission by cracking reaction, and higher Ni content facilitated biodiesel formation. Additionally, Ni (10%)/MgO-Al 2 O 3 catalysts showed excellent reusability and regeneration due to Ni active species, but these advantages were slightly decreased (HCs: from 95.12% to 61.63%; biodiesel: from 75.90% to 57.52%) due to coke deposition and metal active species leaching and oxidation .
Dry reforming of methane (DRM) is a promising pathway to convert greenhouse gas into syngas. However, the commonly used Ni based catalysts suffer deactivation due to severe sintering and coking. In this paper, a series of porous Ni/MgO-ZrO 2 catalysts (5Ni/xM(1-x)Z, x = 0, 20, 40, 60, 80 wt%, respectively) with high specific surface area were synthesized by a facile combustion method followed by incipient impregnation. It is found that the appropriate amount of MgO (40 %) addition in ZrO 2 favors high porosity and high specific area. More MgO enhances the basicity of the catalyst as well as the metal-support interaction (MSI) by the formation of NiO-MgO solid solution, thus improving DRM activity and coking resistance. However, excessive MgO addition leads to over-strong MSI and lower porosity, resulting in lower DRM activity. The catalyst with 40 % MgO addition (5Ni/40M60Z) exhibits the best activity (conversions of CH 4 ∼ 76 %, CO 2 ∼ 83 %) and stability (>50 h) at high GHSV = 96000 ml/g cat ·h and 750 °C. in situ DRIFTS reveals the mechanism that MgO addition improves DRM activity and stability. Compared with ZrO 2 where CO 2 adsorbs as monodentate carbonate, CO 2 tends to adsorb on 40 %MgO-60 %ZrO 2 as bidentate carbonate and then easily transfer to more stable intermediate bidentate formate, thus improving DRM activity and coking resistance. This study provides new insights on the role of Mg addition in Ni/MgO-ZrO 2 DRM catalysts.
Dry reforming of methane (DRM) suffers catalysts deactivation due to severe coking. Ni/MgO-Al 2 O 3 is a promising system for DRM catalysts with high coking resistance, as the addition of MgO in Ni/Al 2 O 3 catalysts can improve the alkalinity of the support and enhance the metal-support interaction. However, so far the activity and stability of Ni/MgO-Al 2 O 3 is still unsatisfactory while the role of Mg addition remains unclear. In this paper, a series Ni 0.5 /xMgO-Al 2 O 3 catalysts with flower-like hollow sphere morphology and high surface area were synthesized via a facile hydrothermal method. Appropriate Mg addition promotes the formation of NiAl 2 O 4 while more Mg addition leads to the formation of Ni x Mg y O. Both cases can enhance the MSI of the catalysts without changing the morphology of the catalyst. More Mg addition also leads to stronger CO 2 adsorption via improving the alkalinity. Nevertheless, overdose of Mg results in weaker MSI and the blockage of Ni active sites. Ni 0.5 /0.5MgO-Al 2 O 3 with moderate Mg addition shows excellent activity (CH 4 ∼ 75 %, CO 2 ∼ 85 %) and stability (>100 h) at a high GHSV = 144000 ml/g cat ·h −1 and 800 °C with nearly no coking formation (<0.8 wt%). This work helps reveal the role of MgO addition in Ni/Al 2 O 3 systems and gives new insights into the design of DRM catalysts with high activity and stability.
Despite significant advances in catalytic activity for CO2 methanation, the catalyst stability has received less attention, limiting its application. This work prepared Ni-supported on MgO-Al2O3 with varying Mg/Al ratio (x) and studied their deactivation mechanism. The deactivation was accelerated by a stability test at 600 °C for 200 h. The activity comparison before and after the stability test reveals that the sample with x = 0.4 shows the best stability without obvious activity decline. While the sample with x = 0.3 is deactivated due to Ni sintering, samples with x = 0.5 and 0.6 are deactivated by the oxidation of Ni, which easily forms a solid solution with excess MgO but is difficult to reduce. That assertion is supported by various characterizations. Such an oxidative deactivation is first-time reported for Ni-based catalysts for CO2 methanation, which could shed light on their rational design and industrial application.
The upgrade of acetone–butanol–ethanol (ABE) mixture from biomass to high-value biofuels has aroused increasing attention. However, a reported heterogeneous catalyst, metal-containing MgAl-hydrotalcite (HT), is confronted with a serious water-resistance problem due to an inherent memory effect of HT materials. With the aim of exploring catalysts with improved water-resistance, metal-containing MgO–SiO2 catalysts were synthesized and evaluated. An investigation on the effect of metal type including Ni, Cu, Fe, Zn, and Co, metal loading, and reaction temperature on catalytic performance indicates that the 10 wt % Ni–MgO–SiO2 catalyst provides the best catalytic performance, giving a yield of 81.5% to C5–C15 ketones and alcohols at 240 °C. As expected, the catalyst exhibits an excellent water-resistance. It could tolerate up to 3 wt % water, which was much higher than 0.5 wt % over that of Cu- or Pd-HT as reported. Results from XRD and 29Si MAS NMR analyses indicate that the high water-resistance could be ascribed to the more stable structure of magnesium silicates formed in the catalyst than HT materials. For a further study of the effect of catalyst property on catalytic performance, 10 wt % Ni–SiO2, 10 wt % Ni–MgO, and 10 wt % Ni–MgO–SiO2 catalysts were investigated and characterized. Results from CO2-TPD, pyridine-IR, and NH3-TPD analyses reveal that the catalytic performance is significantly affected by an acid–base property. Obtaining a high catalytic performance necessitates a cooperation of enough acidic sites and basic sites.
Novel strategies for converting renewable lignin to bulk petrochemicals are highly desirable for achieving sustainable practices in the age of environmental awareness. Herein, we propose an efficient approach for the selective hydrogenolysis of lignin promoted by a cost-effective La3+-doped Ni/MgO catalyst. The results reveal that 84.44% lignin is converted at 270 °C for 4 h, yielding 16.50% volatile products. Importantly, approximately 43.45% of these volatile products are identified as 4-ethyl phenol (7.17% yield), an important intermediate in the fine chemical industry. Intensive analysis of the lignin before and after the reaction confirms that efficient cleavage of the ester linkages is achieved, which correlates directly with the high selectivity of 4-ethyl phenol after a readily decarboxylation reaction. Furthermore, the catalyst characterization demonstrates that La3+ suppresses the formation of a NiMgOx solid solution. Consequently, a greater degree of Ni2+ becomes reducible and the catalyst basicity becomes stronger, both of which are essential for the efficient lignin depolymerization and char reduction. As a result, a significant increase of the yield of volatile products is shown along with a substantial inhibition of biochar formation over the La-doped Ni/MgO catalyst in comparison with that without La doping. Therefore, the present work provides a new insight on producing fine chemicals via a sustainable route.
Novel techniques for upgrading heavy lignin bio-oil, the phenolic oligomer from lignin depolymerization, are of great significance for achieving better utilization efficiency of carbon element in lignin. In this study, we proposed an efficient approach for producing high-quality oxygen-containing fuel from the renewable lignin bio-oil via the C-O bond cleavage and the subsequent hydrogenation over the Cu and Ni supported on alkaline MgO . Noticeably, the optimized Cu 6 Ni 20 /MgO resulted in inspiring yields of ethylbenzene (88.6%) and cyclohexanol (98.3%) from lignin dimers, and a colorless fuel with a high-heating value of 31.4 MJ kg −1 from the realistic lignin bio-oil. The results of catalyst characterization also unveiled that introducing Cu species reduced the formation of NiMgO x solid solution, which increased the content of Ni 0 and consequently promoted the performance of upgrading lignin bio-oil. Furthermore, the recondensation of phenolic oligomers could be effectively restrained by the alkaline MgO. In addition, a plausible mechanism was proposed. Therefore, this work opens a promising avenue to designing efficient strategies for utilizing the heavy components from lignin depolymerization.
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