Surface Basicity Research Articles

Co-Precipitated Ni-Mg-Al Hydrotalcite-Derived Catalyst Promoted with Vanadium for CO2 Methanation.

Co-precipitated Ni-Mg-Al hydrotalcite-derived catalyst promoted with vanadium were synthesized with different V loadings (0–4 wt%) and studied in CO2 methanation. The promotion with V significantly changes textural properties (specific surface area and mesoporosity) and improves the dispersion of nickel. Moreover, the vanadium promotion strongly influences the surface basicity by increasing the total number of basic sites. An optimal loading of 2 wt% leads to the highest activity in CO2 methanation, which is directly correlated with specific surface area, as well as the basic properties of the studied catalysts.

Synthesis of MgO nanostructures through simple hydrogen peroxide treatment for carbon capture

The acceleration of global warming induced by uncontrolled CO2 emission has placed a potential threat to human survival and development. The unique properties of magnesium oxide (MgO) including having appropriate surface basicity, low regeneration temperature and high theoretical CO2 uptake capacity make it a promising adsorbent candidate for CO2 capture. Herein, the development and investigation of structure-activity relationships of MgO nanostructures prepared via simple hydrothermal-calcination synthesis method for CO2 capture were reported in this work. The correlation of structural characteristics and basic site properties of MgO samples were discussed by implementing a variety of analytical technologies including BET, SEM, XRD, TPD, Malvern Mastersizer and XPS. The TPD, XPS analysis as well as Claisen-Schmidt condensation reaction show that the hydrothermal-calcination process strongly reduced crystal size and transformed high, low, and moderate basic sites at different ratios for MgO samples. Particularly, MgO nanostructures with morphology of irregular tiny nanocrystals (down to ~5 nm) prepared from simple hydrogen peroxide (H2O2) treatment on commercial MgO exposed abundant moderate and strong basic sites demonstrated significantly better performance (1.04–1.73 mmol/g in a wide temperature range of 100–300 oC) than commercial MgO for CO2 capture. Recyclability of prepared MgO absorbents was also examined and a simple H2O2 regeneration method was explored. The proper correlation of structural characteristics and basic site properties of MgO samples vs their CO2 capture performance were established.

Influence of basic carbon additives on the electrochemical performance of lead-carbon batteries

Enhancement of the dynamic charge acceptance (DCA) of advanced lead-acid batteries for micro- and mild-hybrid cars is essential to improve the fuel consumption and CO2 emissions by recuperation of the braking energy. In this work, the effect of carbon surface basicity on the electrochemical activity and the DCA of lead-carbon electrodes is revealed. Five different activated carbons (AC) with different pH values ranging from 9.5 to 11.1 were prepared by ammonia and hydrogen gas treatments. These ACs were used as additives in the negative electrodes of 2 V lead-acid cells. The cyclic voltammetry of the pure carbon as well as lead-carbon (negative) electrodes demonstrates that the hydrogen evolution reaction (HER) activity is increased via higher surface basicity of the ACs. A correlation between the surface basicity of carbon and the DCA can be established in the electrochemical performance. A remarkable impact of carbon pH on the charge currents after the charge history (Ic) as well as final DCA (IDCA) is observed. In case of the charge currents after the discharge history (Id) and during simulated Stop/Start microcycles (Ir), the carbon content in the negative electrodes affects the charge currents. This work demonstrates that the DCA of advanced lead-carbon batteries can be improved by using carbon additives with higher pH in the negative electrodes.

Simultaneous production of hydrogen and carbon nanotubes from biogas: On the effect of Ce addition to CoMo/MgO catalyst

In this study, hydrogen and carbon nanotubes (CNTs) are simultaneously produced via a synergistic combined process of CO2 methanation (METH) and chemical vapor deposition (CVD) processes using biogas as a feedstock. METH process could upgrade CO2 containing biogas into CH4-rich gas which then decomposed into H2 and forming CNTs over CoMo/MgO catalyst by CVD process. The effects of Ce addition to CoMo/MgO were investigated. Comprehensive characterization confirms that all as-synthesized samples composed of well-aligned multi-walled carbon nanotubes (MWCNTs) with a narrow size distribution. The Ce addition improved CoMo dispersion on MgO, resulting in smaller and uniform CNTs. The small addition of Ce into CoMo/MgO catalyst could enhance the production CNTs yield. The higher Ce addition would, however, result in the CNTs yield decreased, attributed to a high basicity of CeO2 surface and a large coverage of CeO2 on the catalyst surface. The IG/ID increased with increased Ce addition, while the surface area monotonically decreased, attributed to a decrease in defects of nanotubes. In addition, this wisely combined process could result in a remarkable 100%CO2 elimination, while high CH4 conversion of 90% was obtained. The H2 production yield could gain more than 30 vol% with respect to H2 in the feed stream. The H2 yield and purity in the effluent gas stream were approximately 90%.

Nature of the Pt-Cobalt-Oxide surface interaction and its role in the CO2 Methanation

Based on our previous investigations, it turned out that the Co3O4 material is a promising catalyst in the ambient pressure CO2 methanation. This work aims at understanding the Pt-Cobalt-Oxide surface interaction and its effect on the catalytic performance. The incorporation of Pt nanoparticles into the mesoporous Co3O4 (Pt/m-Co3O4) and commercial Co3O4 (Pt/c-Co3O4) improves the catalytic activity of both catalysts by a factor of ∼ 1.4 and ∼ 1.9 respectively at 673 K. The same tendency towards the increased basicity was also observed. Morphology-induced surface basicity was previously shown to play a key role in determining the catalytic activity of free-standing supports. From HR-TEM (-EDX), EXAFS, CO2-TPD, and CO chemisorption measurements it was established that during the pre-treatment, Co-Pt alloy particles partially covered by the CoxOy layer are formed. It has been postulated that this structure transformation generates new basic centres, the amount of which per unit surface area is significantly larger for Pt/c-Co3O4 and this in turn is responsible for the higher enhancement effect of the Pt/c-Co3O4 catalyst in the CO2 methanation. This study emphasizes the importance of the surface structure exploration for the dynamic catalytic systems in order to reach maximum activity and selectivity in the CO2 methanation.

Zeolites employed as basic catalyst for nucleophilic substitution reactions: An analysis of the adopted approach and hypothesized new perspectives

The present article reports on an excursus of substitution reactions performed on different halo-compounds and several cyclic sulfamidates that are readily accessible to nucleophilic attack. Essentially, a cysteine sulfhydryl group is employed as nucleophile and the process is promoted by the basic sites of activated Zeolites A (4 Å molecular sieves). The catalysis occurs on the external surface of the zeolite, as also assessed by the FT-IR analysis executed on molecules adsorbed on the catalyst. The moderate basicity of the zeolite lattice surface is the prerequisite for conducting chemoselective and in some case stereoselective peptide modifications. The developed methodology allows an efficient one-pot introduction of exogenous moieties into peptides, useful for developing peptidomimetic and/or peptide-based probes.

Diesel reforming to hydrogen over the mesoporous Ni–MgO catalyst synthesized in microfluidic platform

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 MgxNi1-xO (0.5<x < 0.8) with an average particle size in the range of 30.6–35.0 nm in a microfluidic system using a co-precipitation method. Ni particle size, Ni loading, and surface basicity synergistically determine the reforming performance. The Ni(40 wt%)-MgO catalyst demonstrates potential for the SR of n-dodecane, 0# diesel of China national VI standard, methylbenzene, and methylnaphthalene. The deactivation of the catalysts with time-on-stream is mainly attributed to the sintering of Ni nanoparticles; however, it is almost independent of the negligible amount of carbon deposition. Density functional theory calculations verify that for the same active metal particle size, the energy barrier ratio of the forward to reverse reaction of the CH∗ decomposition of the catalyst is smaller with more Ni doped in the MgO.

The Synergistic Character of Highly N‐Doped Coconut–Shell Activated Carbon for Efficient CO2 Capture

AbstractThe coconut shell‐based activated carbon (AC) surface was effectively anchored with amine moieties with acid treatment followed by tetraethylenepentamine (TEPA) anchoring. The activated carbon surface enhanced with basicity is likely to increase the sorbent properties towards CO2 adsorption. The AC surface was modified by varying TEPA concentrations. After amine doping, significant loss in textural property indicates their occupation inside the pores and surfaces. Further, the samples were thermally activated to retrieve the textural properties. The physicochemical properties of modified carbon were characterized using BET, TPD, FT‐IR, Raman spectroscopy and elemental composition. The amine‐modified and thermally activated carbons were tested for CO2 adsorption up to 25 bar at 25 °C. The acid‐base properties of N‐doped carbons were evaluated using isopropanol as a model test reaction at atmospheric pressure. The IPA reaction products of acetone and propene were quantified for their acid‐base nature and correlated to CO2 adsorption capacities. The CO2 adsorption capacity increases by tailoring synergistic properties between surface basicity and micropores. Hence, 20 % TEPA‐derived nitrogen‐enriched carbon reveals a higher yield of acetone 73 %, which in turn enhanced CO2 adsorption capacity of 9.9 mmol/g, and it is found to be a suitable applicant for CO2 capture.

Ammonia as a carrier for hydrogen production by using lanthanum based perovskites

LaNiO3 and LaCoO3 perovskites synthesized by self-combustion were characterised and studied in the ammonia decomposition reaction for obtaining hydrogen. Both the fuel to metal nitrates molar ratio and calcination temperature were found to be crucial to synthesize perovskites by self-combustion. Moreover, generating non-precursor species during synthesis and small metal size were two factors which significantly influenced catalytic activity. Hence, with a citric acid to metal nitrates molar ratio equal to one a LaNiO3 perovskite was obtained with suitable physicochemical properties (specific surface area, lower impurities, and basicity). In addition, a lower calcination temperature (650 °C) resulted in small and well-dispersed Ni0 crystallite size after reduction, which in turn, promoted the catalytic transformation of ammonia into hydrogen. For cobalt perovskites, calcination temperature below 900 °C did not have a significant influence on the size of the metallic cobalt crystallite size. The nickel and cobalt perovskite-derived catalysts, calcined at 650 °C and 750 °C, respectively, yielded excellent H2 production from ammonia decomposition. In particular, at 450 °C almost 100% of the ammonia was converted over the LaNiO3 under study. Furthermore, these materials displayed admirable performance and stability after one day of reaction.

Highly Efficient CO2 Hydrogenation to Methanol over the Mesostructured Cu/AlZnO Catalyst

AbstractIn this work, the mesostructured Cu/AlZnO catalysts were prepared for the CO2 hydrogenation to methanol. Experimental results showed that the weight ratio of Al2O3 and ZnO affected the morphology of the mesoporous AlZnO supports and surface properties of the mesostructured Cu/AlZnO catalysts. The AlZnO‐9 (the Al2O3 mass within the AlZnO support was 90 wt%) with loose spongy porous structure and high surface area facilitated the Cu nanoparticle dispersion. Thus, the Cu/AlZnO‐9 catalyst showed higher exposed Cu surface area (SCu) and more exposed CO2 adsorption sites, which accelerated the CO2 conversion. Meanwhile, the ZnO added into catalysts increased the strength of surface basicity and the surface concentration of Zn species, which promoted the catalytic activity of CO2 hydrogenation to methanol. In addition, the well mesostructure heightened the stability of supported Cu catalyst due to the high dispersion of Cu nanoparticles.

Enhanced low-temperature catalytic performance in CO2 hydrogenation over Mn-promoted NiMgAl catalysts derived from quaternary hydrotalcite-like compounds

Mn-promoted NiMgAl mixed-oxide (NiMnx-LDO, x = 0, 5, 10, 15) catalysts derived from hydrotalcite were synthesized using co-precipitation for CO2 hydrogenation to synthetic natural gas. By regulating Mn contents, NiMn5-LDO delivered the most excellent catalytic performance, being about 2 times higher than that of undoped NiMn0-LDO catalyst (TOF of NiMn5-LDO and NiMn0-LDO: 0.61 s−1 vs 0.31 s−1 @ 240 °C). Through extensive characterization, it was found that Mn dopants promoted the reduction of bulk NiO through tuning the interaction between Ni and Mg(Mn)AlOx support. A high surface ratio of Ni0/Ni2+ was achieved over NiMn5-LDO. Furthermore, the surface basicity strength was tailored by Mn dopants. With 5 wt% of Mn, NiMn5-LDO catalyst showed a stronger medium-strength basicity and higher capacity of CO2 adsorption than others. Particularly, TOF indicates a good correlation with medium-strength basicity over NiMnx-LDO catalysts. The strong metal-support interaction originated from the hydrotalcite structure kept nickel uniformly dispersed, endowing to the improved catalytic performance.

Highly Active Ni Nanoparticles on N‐doped Mesoporous Carbon with Tunable Selectivity for the One‐Pot Transfer Hydroalkylation of Nitroarenes with EtOH in the Absence of H2

AbstractCost‐effective and environmentally friendly conversion of nitroarenes into value‐added products is desirable but still challenging. In this work, highly dispersed Ni nanoparticles (NPs) supported on N‐doped mesoporous carbon (Ni/NC‐x) were synthesized via novel ion exchange‐pyrolysis strategy. Their catalytic performance was investigated for one‐pot transfer hydroalkylation of nitrobenzene (NB) with EtOH in absence of H2. Interestingly, the catalytic performance could be easily manipulated by tuning the morphology and electronic state of Ni NPs via varying the pyrolysis temperature. It was found that the Ni/NC‐650 achieved 100 % nitrobenzene conversion and approx. 90 % selectivity of N,N‐diethyl aniline at 240 °C for 5 h, more active than those of homogeneous catalysts or supported Ni catalysts prepared by impregnation (Ni/NC‐650‐IM, Ni/SiO2). This can be ascribed to the higher dispersion and better reducibility as well as richer surface basicity of the catalyst. More interestingly, the Ni/NC‐650 catalyst achieved complete conversion of various nitroarenes, yielding imines, secondary amines, or tertiary amines selectively by simply controlling the reaction temperature at 180, 200 and 240 °C, respectively. The one‐pot hydrogen‐free process with non‐noble metal catalysts, as demonstrated in this work, shows great promise for selective conversion of nitroarenes with ethanol to various anilines at industrial scale, from an economic, environmental, and safety viewpoint.

Surface Basicity of Metal@TiO2 to Enhance Photocatalytic Efficiency for CO2 Reduction.

Photocatalytic reduction of CO2 to valuable chemical fuels is of broad interest, given its potential to activate stable greenhouse CO2 using renewable energy input. We report how to choose the right metal cocatalysts in combination with the surface basicity of TiO2 to enhance their photocatalytic efficiency for CO2 photoreduction. Uniform ligand-free metal nanoparticles (NPs) of Ag, Cu, Au, Pd, and Pt, supported on TiO2, are active for CO2 photoreduction using water as an electron donor. The group XI metals show a high selectivity to CO and Ag/TiO2 is most active to produce CO at a rate of 5.2 μmol g-1 h-1. The group X metals, e.g., Pd and Pt, mainly generate hydrocarbons including methane and ethane, and Pd/TiO2 is slightly more active in methane production at a rate of 2.4 μmol g-1 h-1. The activity of these photocatalysts can be enhanced by varying the surface basicity of TiO2 with primary amines. However, proton reduction selectivity is greatly enhanced in the presence of amine except amine-modified Ag/TiO2, which shows an activity enhancement by 2.4 times solely for CO2 photoreduction as compared to that without amines without switching its selectivity to proton reduction. Using in situ infrared spectroscopy and CO stripping voltammetry, we demonstrate that the improvement of electron density and the low proton affinity of metal cocatalysts are of key importance in CO2 photoreduction. As a systematic study, our results provide a guideline on the right choice of metals in combination of the surface functionality to tune the photocatalytic efficiency of supported metal NPs on TiO2 for selective CO2 photoreduction.

Preparation and characterization of nanocrystalline NiO by the thermal decomposition of oxalate salts for the dehydrogenation of 2-butanol to methyl ethyl ketone

In the present study, highly active nanocrystalline nickel oxide samples were prepared by using a simple, solvent-free, and cost-effective preparation method. Commercial nickel oxalate dihydrate powder was mixed with deionized water to form a soft paste which was sonicated till dryness and then, calcined in static air. The prepared nickel oxide samples were characterized by means of Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and N2 adsorption-desorption techniques. The surface basicity of the prepared oxide samples was measured by adsorption of CO2 molecules followed by desorption measurements using the thermogravimetry (TG) technique. The catalytic activity of the prepared nickel oxide samples towards the dehydrogenation of 2-butanol to methyl ethyl ketone (MEK) was studied at a temperature range of 225-325°C. The effects of calcination temperature, reaction temperature, and weight hourly space velocity WHSV on the catalytic activity were studied to determine the best calcination temperature and the optimum operating conditions. The sample calcined at 400°C showed the highest activity and the optimum operating conditions were found to be at the reaction temperature of 300°C and WHSV of 15 L h-1 g-1. The selectivity to MEK was higher than 85% for all the conducted experiments.

Oxidation of Toluene on Supported and Unsupported LaCoO3 Perovskites Catalyst

Perovskite type oxide are known to be catalysts for a number of reactions such as total and partial oxidation, hydrocracking, hydrogeneous, hydrogenolysis and reduction etc. Efforts has largely been directed towards synthesis of unsupported and supported perovskites oxides of moderates or high specific area, their bulk and surface properties and their role in heterogenous catalysis. Oxidation of aromatic and aliphatic hydrocarbon over LaMO3 (M=Al, Ni, Mn, Co, Fe, Cr etc.) perovskites have been studied. Vapour phase catalytic oxidation of toluene over perovskites Viz., LaCoO3, LaCoO3/ SiO2 and LaCoO3/Al2O3 has been studied. The characterization of the catalyst was carried out using technique Viz. I.R., Surface area, Packing density. Surface acidity, Surface basicity. The surface area measurements in the temperature range 350ºC to 600ºC. The maximum surface area &amp; maximum activity was observed at 450ºC. The heterogeneous catalytic vapour phase oxidation of toluene give benzaldehyde, benzoic acid, maleic acid and CO2 as products over LaCoO3 and LaCoO3 supported on Al2O3 and SiO2 as catalyst. The LaCoO3 supported on Al2O3 has been found to be the most active and selective catalyst giving 84.0% selectivity for benzaldehyde at 450⁰C with surface area 78.9m2/g. The overall Kinetic analysis indicate that the oxidation of Toluene to benzaldehyde is first order. The order of catalytic reactivity is LaCoO3/Al2O3 &gt; LaCoO3/ SiO2 &gt; LaCoO3.

The role of CO2 in the dehydrogenation of n-octane using Cr-Fe catalysts supported on MgAl2O4

• Fe, Cr and Cr/Fe oxide catalysts studied for dehydrogenation of n -octane with CO 2. • The Fe promoter suppressed hexavalent Cr species by forming a Cr 3+ -O-Fe 3+ matrix. • Excellent stability and selectivity to octenes with 5 wt% Cr 2.5 wt% Fe/MgAl 2 O 4. • Role of CO 2 was oxidative over the Cr and non-oxidative over the Cr/Fe catalysts. The effect of CO 2 on the dehydrogenation of n -octane over Cr-Fe oxides supported on MgAl 2 O 4 (MgAl) was investigated. Addition of Fe as a promoter facilitated the formation of Cr-O-Fe polymeric units, stabilizing the CrO x in the +3 state on the catalysts’ surface. Catalytic results revealed that the 2Cr-Fe catalyst was the most active and also stable (ca. 10 % CO 2 conversion, 8 % n -octane conversion, 84 % selectivity to octene isomers) during a 30 h reaction. The stability and high octenes selectivity over this catalyst was reflected in its higher surface basicity. Based on a redox study using CO 2 , it was found that the dominant mechanism for CO 2 activation was oxidative (Mars van Krevelen) over the monometallic Cr catalyst, while a non-oxidative (Reverse Water Gas Shift) mechanism applied over the nCr-Fe bimetallic catalysts. It is proposed that Cr-O-MgAl is the active site in the monometallic Cr catalyst, while the Cr-O-Fe polymeric units are the active sites in the bimetallic catalysts. Coke deposition was shown to be the major cause of deactivation of the catalysts.

Effect of copper dispersion on SBA-15 and SBA-16 affinity towards carbon dioxide—an approach through thermal programmed desorption

A new approach for the synthesis of zero-valent copper nanoparticles (CuNPs) supported on ordered mesoporous silica SBA-15 and SBA-16 by using vegetal antioxidants, coffee Robusta and green tea was developed in the present work. Diverse characterization techniques such as X-ray diffraction, nitrogen adsorption–desorption, transmission electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy and thermal programmed desorption of CO2 and water allowed stating that the appreciable specific surface area and porosity favor CuNP formation. Copper-loaded SBA-15 and SBA-16 exhibited higher surface basicity and hydrophilic character according to the type of the source of reducing agents and silica framework, respectively. OH-compounds interactions with both CuNP and SBA surface and more particularly with available Si–O-Si groups were found to promote metal dispersion reducing the particle size. The results obtained herein open promising prospects for designing low cost and “green” silica-based materials with judiciously tailored basicity and hydrophilic character for catalysis, adsorption and other surface processes.

Tailoring CO2 adsorption and activation properties of ceria nanocubes by coating with nanometre-thick yttria layers

Ceria (CeO2) is a ubiquitous component in catalysts for environmental protection processes, especially those devoted to CO2 valorisation. Aimed at preparing ceria-based nanomaterials with enhanced CO2 adsorption and activation properties, both the surface acid-base and redox features of ceria nanocubes were modulated by a novel, simple, wet chemistry synthetic strategy consisting of their coating with yttria (Y2O3) layers of variable thickness in the nanometre scale. The as-synthesised samples were characterised with special attention to their surface basicity and reducibility. Characterisation results revealed that the surface doping with yttria not only improved both the reducibility at low temperature and CO2 adsorption capacity of ceria nanocubes, but also introduced a variety of basic sites with different strength. Finally, the careful control of the yttria layer thickness allowed to modulate these effects and thereby the ability of nanostructured ceria to adsorb and activate the CO2 molecule.

Reversible iodine vapor capture using bipyridine-based covalent triazine framework: Experimental and computational investigations

To address the environmental issues arising from the emission of radiotoxic iodine from nuclear waste streams, developing high-capacity and recyclable adsorbents is urgently demanded. In this study, a nitrogen-rich covalent-triazine framework (CTF-bpy) was synthesized through the ionothermal synthetic method and was used as a reusable adsorbent to capture iodine vapor for sequential cycles. The obtained CTF-bpy adsorbent showed ultrahigh iodine vapor capture capacity of 4.52 g.g−1 at 90 °C and atmospheric pressure, which ranks among the highest values reported to date. CTF-bpy could be simply recycled by washing and heating while preserving above 89.6% of its initial iodine capture capacity after five consecutive cycles, demonstrating its excellent structural stability. Assessment of the adsorption kinetics of the iodine vapor through the fractal-like pseudo-first-order (FL-PFO) kinetic model revealed that the diffusion through micropores was the rate-controlling mechanism. Moreover, the density functional theory (DFT) calculations further demonstrated the significance of the surface's basicity and aromaticity of the structure in efficiently capturing the iodine species. This study may shed light on designing and developing novel adsorbents suitable for solving one of the main environmental issues.

Carboxymethylation of cinnamylalcohol with dimethyl carbonate over the slag-based catalysts

The carboxymethylation of cinnamylalcohol with dimethyl carbonate was performed using low-cost catalysts obtained from desulfurization slag. Processing of steel slag performed by different techniques was resulted in a wide range of the catalysts with different morphological and structural properties. Catalytic evaluation of the slag catalysts illustrated diversity of the obtained results strongly dependent on the surface area, crystal morphology and basicity. Catalytic materials demonstrated high variability of the conversion (8–85%) exhibiting similar selectivity to the desired product – cinnamyl methyl carbonate (ca. 80%). A significant impact of ultrasonication on catalytic activity was observed. Comparison of the synthesized samples with commercial basic materials illustrated competitive ability of the slag catalysts. Based on the results of catalytic evaluation and product analysis the reaction network was proposed and verified by thermodynamic analysis. A kinetic model was developed to describe concentration dependencies in carboxymethylation.