•Nd-containing mesoporous silica support xNdMS were prepared by sol–gel method.•Positive effect of Nd on structural properties of Ni/xNdMS was investigated.•Ni/xNdMS catalysts exhibited high catalytic performance in OCRM and DRM reactions.•The oxidation state and the nickel particle size affected the activity.Ordered mesoporous silica materials based on nickel and other elements have been extensively studied because controlling the size of metal nanoparticles is an effective method to tune the superficial physicochemical process. Neodymium (Nd)-promoted mesoporous silica xNdMS (x: molar ratio of Nd/Si = 0.01, 0.02, 0.04, 0.06) were prepared through a sol–gel strategy. Nickel-based catalysts with high dispersion by using xNdMS as supports were investigated for methane reforming with carbon dioxide and/or oxygen to produce syngas. xNdMS supports and nickel catalysts were examined by combining textural, structural, local and surface information. The characterization results showed that Nd was successfully incorporated into the mesoporous framework of MS and Nd was beneficial to improve the metal dispersion. All Nd-promoted Ni/MS catalysts were effective for the methane reforming reaction. Ni/0.04NdMS catalyst exhibited the highest initial catalytic activity during 12 h time on stream, which was attributed to its high metal dispersion, more basic sites and the strengthened nickel-support interaction. The readily deactivation and poorest catalytic activity of Ni/MS catalyst were due to the serious oxidation of metallic nickel under reaction medium.Download high-res image (254KB)Download full-size image

•Impregnation strategy of Y2O3 addition on Ni/Al2O3 and Co/Al2O3 catalysts.•Positive effect of Y2O3 on Ni/Al2O3 and negative effect of Y2O3 on Co/Al2O3.•Ni/YAl2O3 exhibited better activity and stability compared to Ni + Y/Al2O3.•Co/YAl2O3 showed the largest amount of carbon deposit and metal sintering.The overall purpose of this study was to develop an effective catalyst with high carbon resistance in the conversion of methane to synthesis gas via dry reforming. The catalytic performances of α-Al2O3 supported nickel- and cobalt-based catalysts modified with Y2O3 were investigated in this process. Sequential impregnation and co-impregnation of Y2O3 addition were employed during the catalyst preparation. The modification effect of Y2O3 and the preparation strategies on the surface structure, physico-chemical properties and coke deposition were revealed. For nickel catalysts, two impregnation methods of yttrium addition both greatly increased the activity and stability compared with counterpart Ni catalyst. Furthermore, the best performance over Ni/YAl2O3 catalyst prepared by sequential impregnation was related to smaller metallic nickel particle and more basic sites, while its remarkable stability was due to the small degree of graphitization and the less amount of carbon deposit. This sintering-resistant and higher carbon-resistant nickel catalyst is potentially useful for methane conversion in high reaction temperature. On the contrary, the negative effect of Y2O3 was clearly found for Co/Al2O3 catalyst. The introduction of Y2O3 led to inadequate reduction and metal sintering in reduced and spent catalysts. Co/YAl2O3 prepared by sequential impregnation exhibited steep deactivation during the methane reforming reaction because of the obvious cobalt sintering and serious carbon deposition.

•Synergic modification by EG and CA favored better distribution of Ni particles.•Synergic modification prevented Ni aggregation in high reaction temperature.•EG showed better alcohol property for pretreating silica support.•EG improved the supported metal species to interact with the isolated SiOH.•Adding appropriate CA into the impregnation solution favored Ni dispersion.This study targeted the novel silica-supported nickel-based catalyst (Ni/SiO2) modified by organic agents. The synergic modification effect of ethylene glycol (EG) and citric acid (CA) on the nickel catalyst was investigated. EG was used to pretreat the silica support and CA was used in the impregnation solution to synthesize the nickel based catalysts with different CA loadings. NiCA-x/SiO2-EG (x: molar ratio of CA/Ni ranging from 0.25 to 1.5) catalysts achieved an excellent stability and higher catalytic activity than the catalysts without EG in oxidative CO2 reforming of methane (CH4/CO2/O2 = 40/20/10, total flow rate = 60 ml/min, reaction temperature = 750 °C, and reaction pressure = 1 atm). EG addition modified the surface properties of silica support. The use of CA in the impregnation solution had a clear effect on the dispersion of NiO and Ni in the silica matrix. For the catalysts with the same content of CA, the catalysts with EG modification showed the synergic effect of EG and CA by improving the chemical interaction between Ni and support, resulting in higher dispersion of nickel. The temperature programmed reduction revealed that the reduction peak shifted to higher temperature with increasing CA loading, which was attributed to the smaller metallic Ni size of the reduced catalysts. The transmission electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy confirmed that the addition of organic additive modified the silica surface and retained the metallic Ni species, and thus preventing the metal aggregation at high reaction temperature. The NiCA-1.5/SiO2-EG catalyst exhibited the highest activity, which was due to the small metallic metal size (4 nm) and the strong interaction between silica support and metal species.

•DFT study was conducted for CH3OH dehydrogenation on PtPd3(111) surface.•The most favorable reaction pathway for CH3OH dehydrogenation was clarified.•CH3OH was dehydrogenated to generate CH3O* intermediate via O–H cleavage.•The proposed pathway was favorable at both kinetic and thermodynamic levels.Platinum (Pt)-based catalyst has been widely used as the catalyst in direct methanol fuel cells. This study aimed at determining the favorable pathway for methanol (CH3OH) dehydrogenation on the PtPd3(111) surface through the periodic density functional theory (DFT) calculation. The calculation evaluated the stable adsorption configurations of the possible intermediates produced from the successive dehydrogenation of methanol through C–H and O–H bond scission. The results showed that CH3OH, CH2OH, CH3O and CHO preferred to locate at the top site, COH, CO and H preferred to adsorb on the face centered cubic (fcc) site, while CH2O and CHOH would choose the bridge site. Both CH3OH and CH2O were bonded weakly on the PtPd3(111) surface due to their closed-shell electronic configurations. The other intermediate species were interacted strongly with the surface. The energy barriers in four possible pathways via initial breakage of O–H or C–H bond were calculated. By comparing the energy changes in the potential energy surface, the initial O–H scission of CH3OH as the most favorable reaction pathway was determined. The activation barrier by this pathway was only 0.955 eV. The dehydrogenation mechanism from CH3OH to CO via breaking O–H bond was derived as CH3OH → CH3O → CH2O → CHO → CO. The first dissociation step, CH3OH into CH3O and H was identified as the rate-limiting step. The theoretical results indicated that the proposed pathway for methanol dehydrogenation on PtPd3(111) surface was energetically favorable, and verified that the PtPd3 catalyst with Pt monolayer is a good candidate for methanol dissociation.

•Carbon cloth was modified electrochemically using three solutions.•Surface modification enhanced bacterial adhesion and reduced ohmic resistance.•Modification with HNO3/H2SO4 showed the highest current/power generation.•PCA analysis showed positive effects of modification on MFC start up.Anode modification was explored as an approach to enhance the startup and improve the performance of microbial fuel cells (MFCs) inoculated with mixed cultures for wastewater treatment. Carbon cloth (CC) anodes were modified by electrochemical oxidation in three electrolytes: nitric acid + sulfuric acid (CC-NS), ammonium nitrate (CC-AN), and ammonium sulfate (CC-AS). The acidic modification of the anode material increased in the ratio of saturated/unsaturated carbon on the surface and consequently, a decrease in electrode resistance was observed. A linear dependence between the MFCs operational characteristics and the anodes resistance (R2 ≥ 0.9) indicated the dominating role of this parameter. This modification also enhanced the bacterial attachment (wet and dry biomass) and biofilm formation. CC-NS, CC-AS and CC-AN anodes accelerated the start up period of the MFCs and demonstrated higher current and power compared to the unmodified CC. The differences in MFCs electrochemical behavior tended to decrease with time. Principal Components Analysis (PCA) was used to identify the parameters having major influence on the system performance, and the results underlined the positive effect of the surface modification on the MFCs output due to increases in the amounts of unsaturated and oxidized carbon, Electrochemical Accessible Surface Area (ECSA) and bacterial attachment.

•Co/CNTs was effective for epoxidation of styrene.•The structure of the oxidant was crucial for the epoxidation of styrene.•The nature of the solvent affected the catalytic activity and the selectivity.Cobalt supported on carbon nanotubes (Co/CNTs) was developed as a novel cost-effective catalyst by impregnating CNTs in metallic precursor solution. The structures of the Co/CNTs catalysts were extensively characterized, and the presence of nanometer-sized Co particles was confirmed. The activity of Co/CNTs catalysts were examined for the epoxidation of styrene with tert-butyl hydroperoxide (TBHP) as the oxidant. The results showed that the catalytic behavior of Co/CNTs catalysts was closely correlated with the nature of oxidants, the structure of supports, and the polarity of the solvents. Compared with hydrogen peroxide, TBHP was a better oxidant for the epoxidation of styrene with the Co/CNTs catalyst, due to the lower dissociation energy. The favorable catalytic performance was obtained in acetonitrile solvent. The oxygen species with a radical nature activated by TBHP on the Co(II) site was proposed for the epoxidation reaction. This study also demonstrated that Co/CNTs catalysts were stable and could be reused without significant loss of activity.The activity of cobalt catalysts supported on carbon nanotubes were examined for the oxidation of styrene using TBHP as oxidant. The catalytic behavior of cobalt catalysts was strongly dependent on the nature of oxidants, the structure of supports and polarity of the solvents. The cobalt catalysts were stable and could be reused without significant loss of activity.

•Yttrium-doped SBA-15 mesoporous supports were prepared via sol–gel method.•Y-containing nickel catalysts were effective for CH4 reforming with CO2.•Y enhanced the reduction of NiO and the formation of smaller Ni0 particles.A series of mesoporous yttrium (Y)-containing SBA-15 (mesoporous silica of Santa Barbara Amorphous type material) prepared using a sol–gel method with various Y/Si molar ratios was investigated as the supporting material of nickel (Ni) catalysts for the methane reforming with CO2. The highly ordered hexagonal structure of SBA-15 was well-retained after the incorporation of yttrium at the molar ratio of Y/Si (0.04). The presence of yttrium in the framework of SBA-15 in Ni catalysts effectively enhanced the formation of the Ni metallic particles with small size. It also significantly promoted the reduction of NiO due to the oxygen vacancies on the surface of the yttrium-containing SBA-15 supports, and the high mobility of the surface oxygen species. All yttrium-containing nickel catalysts were effective for the methane reforming with CO2. The supported Ni catalyst with Y/Si molar ratio of 0.04 exhibited the highest activity, which was due to its highly ordered mesoporous structure, large pore diameter and small metallic metal size.

A series of nickel-based catalyst supported on silica (Ni/SiO2) with different loading of Ce/Ni (molar ratio ranging from 0.17 to 0.84) were prepared using conventional co-impregnation method and were applied to synthesis gas production in the combination of CO2 reforming with partial oxidation of methane. Among the cerium-containing catalysts, the cerium-rich ones exhibited the higher activity and stability than the cerium-low ones. The temperature-programmed reduction (TPR) and UV–vis diffuse reflectance spectroscopy (UV–vis DRS) analysis revealed that the addition of CeO2 reduced the chemical interaction between Ni and support, resulting in an increase in reducibility and dispersion of Ni. Over NiCe-x/SiO2 (x = 0.17, 0.50, 0.67, 0.84) catalysts, the reduction peak in TPR profiles shifted to the higher temperature with increasing Ce/Ni molar ratio, which was attributed to the smaller metallic nickel size of the reduced catalysts. The transmission electron microscopy (TEM) and X-ray diffraction (XRD) for the post-reaction catalysts confirmed that the promoter retained the metallic nickel species and prevented the metal particle growth at high reaction temperature. The NiCe-0.84/SiO2 catalyst with small Ni particle size exhibited the stable activity with the constant H2/CO molar ratio of 1.2 during 6-h reaction in the combination of CO2 reforming with partial oxidation of methane at 850 °C and atmospheric pressure.Highlights► Ce-promoted Ni/SiO2 catalysts showed high catalytic activity and good stability. ► The Ni/SiO2 doped with Ce had smaller Ni0 particles than undoped one. ► Ce plays a key role in keeping the Ni0 particle and preventing the aggregation.