Short-channel SBA-15 Research Articles

Immobilization of gold on short-channel mesoporous SBA-15 functionalized with thiol and hydrophobic groups for oxidation reactions

Abstract Nanosized gold entities immobilized on short-channel SBA-15 mesoporous materials functionalized solely with mercaptopropyl groups and together with propyl and octyl moieties have been prepared following a two-steps procedure. These materials have been used as catalysts for the oxidation of cyclohexene with molecular oxygen in liquid phase at atmospheric pressure. First, SBA-15 materials functionalized only with mercaptopropyl groups and with a combination of these groups with two hydrophobic moieties, namely propyl and octyl, have been synthesized in the presence of the non-ionic surfactant P104. Small particles having short channel length have been identified by TEM and SEM. In order to study the influence of the nature of the sulphur functional group, these S-bearing materials were also oxidized with hydrogen peroxide or dimethyldioxirane (DMD) to sulfonic groups prior to gold immobilization. The effectiveness of these oxidation methods was assessed by 29Si MAS NMR, 13C CP MAS NMR, XPS, chemical and thermal analysis, and it has been found that DMD oxidized efficiently thiol groups to sulfonic groups, but H2O2 leaves a fraction of unreacted thiol. In a second step, nanosized gold entities have been prepared by a two-liquid phases route involving rosemary oil as organic phase and an aqueous phase formed by dissolving gold in a solution of ammonium chloride in concentrated nitric acid (aqua regia). Following this method, a fraction of the Au dissolved in the aqua regia solution is spontaneously reduced and transferred to the essential oil phase. Upon contacting the gold-bearing organic layer with the mesoporous materials, gold is actually immobilized on them, rendering metal contents in the range 1.1-0.2 wt.%, being those functionalized with alkyl chains the least efficient in capturing gold from the organic phase. No surface plasmon resonance band at 520 nm characteristic of gold nanoparticles has been detected by UV–vis spectroscopy in these Au-containing materials. All of them are active and selective for the allylic oxidation of cyclohexene, but their specific activity varies as a function of the nature of the functional groups. It has been found that the most active catalysts are those pre-oxidized with DMD. The presence of hydrophobic octyl groups increases substantially the turnover number of the reaction (TON), while the short-chain propyl moieties hardly affect the activity. It has been found that the nanosized gold entities initially present in the catalysts evolve in the reaction medium towards the formation of nanoparticles.

Gold-copper catalysts supported on SBA-15 with long and short channels – Characterization and the use in propene oxidation

Gold and copper were supported on short-channel SBA-15 and conventional long-channel SBA-15 for selective oxidation of propene with molecular oxygen. The obtained materials were characterized by several techniques (N2 adsorption, XRD, UV–vis, XPS, XAS) and tested as catalysts in propene oxidation with molecular oxygen. The influence of the following parameters on the catalytic activity and the product selectivity to acrolein was considered: i) the length of channels in SBA-15 which determined the particle size of active species and diffusion of the reaction substrates / products, ii) the conditions in which copper-gold alloy-like structure was formed, iii) the effect of gold and copper on the reaction pathway, iv) the changes on the catalyst surface caused by the oxidation of propene and v) the role of acidity on the reaction selectivity. One of the most important findings from this work was the evaluation of the conditions in which copper and gold species were introduced to be in vicinity which led to the effective oxidation of propene to acrolein. It was found that such a vicinity can be achieved by gold-copper alloy formation during hydrogen reduction and next separation of the two components upon exposure to the reaction conditions. The reaction pathway was also considered and discussed.

The influence of Zr presence in short channel SBA-15 on state and activity of metallic modifiers (Ag, Au, Cu, Fe)

Abstract Mesoporous silicas, SBA-15, synthesized with the addition of zirconium oxychloride (ZrOCl2) which ensures obtaining short channels, were used as supports for metallic modifiers including silver, copper, gold and iron. Different preparation routes of these materials, denoted as SBA-S (S stands for short channels), resulted in different morphologies and different contents of zirconium left after the preparation. Samples SBA-S1 and SBA-S2 were obtained after treatment with sulfuric acid (leaching of ca. 98.5% of zirconium ions), whereas SBA-S3 was not treated with H2SO4, which resulted in a higher zirconium content. Metallic catalysts were prepared by grafting of metal species on organosilane functionalized supports. Characterizations by X-ray diffraction, ultraviolet–visible spectroscopy and X-ray photoelectron spectroscopy allowed determination of the oxidation state of metallic modifiers and evidenced the interactions between the modifier (Ag, Au, Cu, Fe) and the zirconium that remained in the silica support. The reaction of 2-propanol decomposition and Fourier-transform infrared spectroscopy combined with adsorption of pyridine clearly showed the effect of zirconium on surface properties of metallic catalysts. Strong acidic Zr4+ species modified the surface acidic-basic properties of the catalysts. This phenomenon should be taken into account when the SBA-S materials are used as supports for potential catalytic applications. The reference material was the long channel SBA-15 (denoted as SBA-L) prepared and modified with metals by the same routes as the short channel materials.

Thiol functionalization of short channel SBA-15 through a safe, mild and facile method and application for the removal of mercury (II)

To avoid the dangerous operational conditions, shorten the preparation time and improve the adsorption performance of common mesoporous SBA-15, a highly ordered short channel SBA-15 was successfully functionalized with thiol group (SH) by a safe, mild and facile hydrothermal method without the addition of any acetone or toluene. The as-prepared thiol functionalized SBA-15-SH material was characterized by various means and applied for the removal of heavy metal of mercury (Hg(II)) from aqueous solution. The results indicated that the preparation process of thiol functionalization of SBA-15 was greatly shortened from 24–48 h to about 15 h. The adsorption of heavy metal Hg(II) with prepared SBA-15-SH material presented a high adsorption capacity of 195.6 mg/g at pH of 8 and had a good correlation with the pseudo-second-order and Freundlich models. Moreover, the removal process of Hg(II) was endothermic and spontaneous. The characterization of SBA-15-SH material before and after adsorption showed that the chemical combination of thiol and Hg(II) ions through covalent bond and electrostatic attraction were the main removal way of Hg(II). The good reusability, economy and hydrothermal stability further displayed that the resultant SBA-15-SH material can be a promising adsorbent for the removal of heavy metals from aqueous solution in practical application.

Granulation of short channel SBA-15 adsorbent and application for the removal of U(VI) by packed column

In order to reduce the loss of particles during the cycling operation, a technology for the granulation of short channel SBA-15 adsorbent was developed. The adsorption behavior of obtained granules was studied under various factors including initial pH value, contact time in different initial concentration and acid stability by batch experiments. A continuous packed column loaded with granules was performed to remove U(VI) from aqueous solution. The uranium concentration was highly enriched than feed solution. The granules packed in column exhibited excellent reusability through cycling test. The result showed promising application prospect in the uranium extraction from aqueous solution.

Short channeled Ni-Co/SBA-15 catalysts for highly selective hydrogenation of biomass-derived furfural to tetrahydrofurfuryl alcohol

Liquid phase and one-step reaction for furfural (FFR) hydrogenated to tetrahydrofurfuryl alcohol (THFA) was conducted by employing noble metal-absence and toxicity-free, bimetallic Ni-Co catalysts. The bimetallic Ni-Co catalysts with different molar ratio of Ni to Co and two monometallic catalysts (Ni, Co) were synthesized by conventional incipient-wetness impregnation method with short channeled SBA-15 as support. Among these catalysts, highly selective hydrogenation of FFR to THFA was attained over Ni-Co/SBA-15 catalysts. The impact of molar ratio of Ni/Co was studied with a fixed Ni loading (10 wt %) in bare support. The samples were characterized by N2 sorption, XRD, XPS, H2-TPR, SEM, TEM and CO chemisorption. The results confirmed that the reducibility of Ni-catalysts can be improved by incorporating Co metal and revealed that appropriate amount of spinel NiCo2O4 oxides is favorable to uniform and high dispersion of Ni0 and CoO over short channeled SBA-15, which would be benefit for the catalytic performance. For catalytic activity investigation, other four mesoporous SiO2 materials (MCM-41, MCM-4, MCF-2 and common SBA-15) were employed as supports to investigate the effect on the hydrogenation of FFR and the reaction parameters including the reaction temperature, initial of H2 pressure, reaction time and the reusability of the catalysts were also studied. 100% of FFR conversion and 92.1% of THFA selectivity were achieved at 90 °C, 50 bar of initial H2 and 2.0 h over catalyst Ni-Co/SBA-15 when the molar ratio of Ni to Co was 0.67.

New short-channel SBA-15 mesoporous silicas functionalized with polyazamacrocyclic ligands for selective capturing of palladium ions in HNO3media

Novel polyazamacrocyclic ligand decorated short-channel mesoporous silicas with the ability to selectively capture palladium ions in HNO3solutions.

Oxygen-containing/amino groups bifunctionalized SBA-15 toward efficient removal of methylene blue: kinetics, isotherm and mechanism analysis

Bifunctionalized SBA-15 with oxygen-containing/amino groups (NH2-SBA15-ox) has been synthesized using a sequential processing strategy: (1) direct conversion of P123 organic surfactant into a thin carbon layer on the interior framework of short-channeled SBA-15 (C-SBA-15), (2) as-prepared C-SBA-15 was then fully oxidized with (NH4)2S2O8 (C-SBA15-ox) and (3) the C-SBA15-ox was post-modified via treatment with APTMS, which created a high density of amino functional group mainly on the external surface of platelet particles. It was shown that bifunctionalized SBA-15 demonstrated much improved adsorption performance toward methylene blue under adsorption testing conditions. Specifically, the adsorption equilibrium time was significantly reduced from 180 min (initial SBA-15) to 60 min (C-SBA15-ox) and then to no more than 10 min (NH2-SBA15-ox); the maximum adsorption capacity was increased from 157 mg/g (initial SBA-15) to 379 mg/g (C-SBA15-ox) and then to 445 mg/g (NH2-SBA15-ox). In combination of short-channeled framework and bifunctionalized surface groups, the NH2-SBA15-ox should be considered as a potential adsorbent to remove other toxic substances from wastewater. Integration of oxygen-containing/amino functional surface group and platelet morphology endowed SBA-15-like sorbents with high affinity and fast adsorption kinetics toward methylene blue from aqueous solution.