Homogeneous Deposition Precipitation Research Articles

Cu/SiO2 catalysts prepared by hom- and heterogeneous deposition–precipitation methods: Texture, structure, and catalytic performance in the hydrogenolysis of glycerol to 1,2-propanediol

Cu/SiO2 catalysts prepared by homogeneous deposition–precipitation (Hom-DP) and heterogeneous deposition–precipitation (Het-DP) methods have been systematically characterized focusing on the effect of precipitation manner during catalyst preparation. It is found that the texture, structure and composition of the dried, calcined and reduced catalysts were largely affected by the precipitation manner. Based on characterizations and previous findings, the copper species on the dried, calcined, and reduced catalysts as well as on the catalysts after work were assigned. Due to a homogeneous precipitation manner, the catalyst prepared by Hom-DP method presented a much higher dispersion, a smaller copper particle size and thus a larger copper surface area than those of its counterpart prepared by Het-DP method. Unexpectedly, catalytic activity tests in the hydrogenolysis of glycerol showed that the catalyst prepared by Het-DP method inversely surpassed the former catalyst, mainly due to a larger number of copper species in the Het-DP catalyst was prereduced to active Cu0 sites, which also presented remarkably higher stability during aqueous phase glycerol reaction as compared to those in the former catalyst. In addition, the selectivity to 1,2-propanediol product is found to be affected by both the precipitation agent applied and the structure of the catalysts.

Solvent-free selective oxidation of primary alcohols-to-aldehydes and aldehydes-to-carboxylic acids by molecular oxygen over MgO-supported nano-gold catalyst

Magnesium oxide supported nano-gold catalyst (prepared by the homogeneous deposition precipitation technique) showed high activity/selectivity and excellent reusability in the oxidation of different primary alcohols and aldehydes to corresponding aldehydes and carboxylic acids, respectively, by molecular oxygen (under atmospheric pressure) in the absence of any solvent. Influence of the catalyst calcination temperature (400–900 °C), reaction temperature (50–120 °C) and use of different solvents (viz. toluene, p-xylene, DMF or DMSO) on the oxidation reaction has also been studied.

Heteroepitaxial growth of gold on flowerlike magnetite: An efficacious and magnetically recyclable catalyst for chemoselective hydrogenation of crotonaldehyde to crotyl alcohol

Au/Fe 3O 4 catalysts with flowerlike and particulate morphologies have been prepared by homogeneous deposition–precipitation of gold on hematite materials synthesized in different ways, followed by integrative reduction. HRTEM revealed the heteroepitaxial growth of gold crystallites on flowerlike magnetite materials along the {1 1 1} planes, which may account for their smaller and more uniform gold nanoparticles. The stronger metal-support interaction on flowerlike Au/Fe 3O 4 catalysts was also manifested by the higher reduction temperature of gold than that on particulate magnetite-supported catalysts. In liquid phase hydrogenation of crotonaldehyde, the flowerlike Au/Fe 3O 4 catalysts show high selectivity (⩾76%) in the entire reaction course and high yield (⩾75%) to crotyl alcohol. They also display excellent separation and recycling characteristics. A perimeter interface mechanism involving the hydroxyl groups on magnetite and the positively charged gold atoms linked to the lattice oxygen of magnetite is established to address the remarkably high selectivity over the flowerlike Au/Fe 3O 4 catalysts.

Highly Sensitive Methane Sensors Based on Pd/HMS and Pd/SBA-15 Composite Prepared by Homogeneous Deposition-Precipitation Method

Highly Sensitive Methane Sensors Based on Pd/HMS and Pd/SBA-15 Composite Prepared by Homogeneous Deposition-Precipitation Method

Low Temperature Water-Gas Shift Reaction on Au-CeO2/Al2O3 Catalysts

The low temperature water gas shift activities of Au-CeO2/Al2O3 catalysts were studied in this work. The catalysts were prepared by impregnation of CeO2 on alumina support followed by the homogeneous deposition precipitation of Au on CeO2/Al2O3. The catalysts were tested in a microflow reaction system. It was found that the activity of the catalyst increased with increasing Ce loading from 2.5 wt.% to 10 wt.% significantly while the increase in the activity was minor with the further increase of the ceria to 20 wt.%. The increasing Au content from 1 wt.% to 3 wt.% inversely affected the activity but the conversion increased with increasing Au to 5 wt.%. It was observed that the activity of 5wt.%Au/20wt.%Ce/Al2O3 decreased with increasing CO concentration. On the other hand, the CO conversion was increased with increasing H2O in the feed (significantly up to 10% H2O and then slightly after that). The 15% CO2 in the feed decreased catalytic activity slightly while the negative effect of 60% H2 was more dramatic. The presence of both CO2 and H2 in the feed together resulted the lowest conversion as expected.

Ruthenium catalyst on carbon nanofiber support layers for use in silicon-based structured microreactors, Part I: Preparation and characterization

The preparation and characterization of ruthenium catalytic nanoparticles on carbon nanofiber (CNF) support layers via homogeneous deposition precipitation (HDP) and pulsed laser deposition (PLD) is presented. Prior to ruthenium deposition the CNF layers were functionalized via liquid phase oxidation treatment using nitric acid at 90°C. This acid treatment not only effectively removed accessible CNF-growth catalyst, but also resulted in the formation of oxygen containing functional groups on the external surface of CNFs. A variety of characterization techniques, viz. TEM, XRD, XRF, XPS, and point-of-zero-charge (PZC) measurements were used to analyze the influence of the oxidation pretreatment on physico-chemical properties of CNF layers qualitatively and quantitatively. HDP yielded a very sharp size distribution (∼85% of the particles had a diameter of 1.0–1.5nm), whereas PLD had a less narrow distribution (the diameter of ∼75% of the particles was 1–3nm). Both methods yielded a ruthenium loading of 2.3±0.1wt.%, and in particular HDP showed uniform anchoring of particles throughout the thickness of the CNF layer. Using optimal conditions, the space in a silicon-based microreactor channel was efficiently filled with open, entangled CNF layer, which were used as anchor points for Ru using HDP and PLD.

Carbon nanofiber growth on carbon paper for proton exchange membrane fuel cells

Homogeneous deposition precipitation (HDP) of nickel has been investigated for the growth of carbon nanofibers (CNFs) on carbon paper for use in proton exchange membrane fuel cells as a gas diffusion layer. Selective CNF growth on only one side of carbon paper is required to transfer the generated protons on platinum catalyst fast enough to avoid any proton mass transfer losses. For this purpose, a mask deposition holder was designed to deposit the nickel hydroxide which is reduced to nickel with hydrogen before catalyzing the CNF growth. The deposition time effect on the catalyst loading and the effect of the catalyst loading variation on the yield of CNF growth on carbon paper were investigated. Both effects had linear dependence in the region of interest. The HDP of nickel on the carbon paper ensured strong attachment of nickel crystals on the carbon paper fibers keeping the porosity at a promising level with an acceptable BET area of CNFs. The HDP method provides fine-tuning in the CNF layer thickness only on one side of the carbon paper with good reproducibility in the deposition of nickel.

Copper–manganese oxide catalysts supported on alumina: Physicochemical features and catalytic performances in the aerobic oxidation of benzyl alcohol

We report the facile synthesis of alumina supported copper–manganese mixed oxide catalysts by a homogeneous deposition–precipitation method and the catalytic applications of these catalysts in the oxidation of benzyl alcohol using molecular oxygen. Benzyl alcohol conversion of ca. 90.9% was achieved with benzaldehyde as the main product. The catalyst can be recycled consecutively up to seven runs without appreciable loss of its activity and selectivity. Characterizations with X-ray diffraction, transmission electron microscopy, Raman, X-ray absorption spectroscopy, and hydrogen temperature-programmed reduction suggested the formation of a mixed oxide (Mn 1.5Cu 1.5O 4) microcrystalline phase after adding copper to the manganese supported on alumina. Such formation would account for the high catalytic performance. Calcination under high temperature decomposed this mixed oxide phase, resulting in a poor catalytic activity.

Effect of noble metals deposition on the catalytic activity of MAPO-5 catalysts for the reduction of NO by CO

Molecular sieves MAPO-5 (M: Co, Ti, Cr and Fe) with the AFI structure type were prepared by the hydrothermal method. Noble metals (Pd, Rh, Ir and Ru) were deposited on the molecular sieve supports using the homogeneous deposition precipitation method. The catalysts were characterized using XRD, TEM, DRUV-VIS, N 2 sorption, SEM, TG/DTA and ICP analysis techniques. The PdO and RhO x species demonstrated small particle sizes as compared with other noble metals. The catalysts were evaluated for their performance in the reduction of NO by CO at different temperatures (150–500 °C) for a GHSV of 44,000 h −1. Among the palladium and noble metals deposited catalysts, the PdCoAPO-5 and RhCoAPO-5 showed excellent performance. For the RhCoAPO-5 (Rh loading = 2.98% and Rh particle size = 2.2 nm) catalyst, the temperature required for complete NO reduction was 210 °C, which is lower than that required for PdCoAPO-5 (Pd loading = 2.96% and Pd particle size = 4 nm) and IrCoAPO-5 (Ir loading = 2.89% and Ir particle size = 6.5 nm) under identical conditions. The Rh deposited CoAPO-5 catalyst effectively operated at lower temperatures as compared with the other noble metal deposited CoAPO-5 catalysts studied here.

Solvent-free selective oxidation of benzyl alcohol to benzaldehyde by tert-butyl hydroperoxide over U 3O 8-supported nano-gold catalysts

Liquid-phase oxidation of benzyl alcohol to benzaldehyde by tertiary butyl hydroperoxide over different uranium oxide supported nano-gold catalysts in the absence of a solvent has been thoroughly investigated. The influences of catalyst parameters [viz. method of gold deposition (impregnation, co-precipitation, deposition–precipitation and homogeneous deposition–precipitation), gold loading (0–8 wt%) and catalyst calcination temperature (100–900 °C)] on the catalyst performance have been investigated. The influence of reaction conditions [viz. reaction time (0–2 h) and temperature (25–94 °C)] on the process performance has also been studied. The Au/U 3O 8 catalyst prepared by the homogeneous deposition–precipitation and calcined at 400 °C showed very high activity (100% benzyl alcohol conversion with >85% selectivity for benzaldehyde) in the process for a short reaction period (0.5 h) at 94 °C. The catalyst also showed excellent reusability in the process.

Formation of acid sites in amorphous silica-alumina

A suite of amorphous silica-aluminas (ASAs) was prepared by homogeneous deposition–precipitation (HDP) of aluminium on a silica surface followed by calcination. The HDP process was investigated in detail by 27Al NMR spectroscopy of solid and liquid aliquots of the synthesis mixture. Deposition occurs predominantly via a hydrolytic adsorption of aluminium onto the hydroxyl groups of the silica surface. Precipitation becomes more significant at higher aluminium concentration. Depending on the aluminium loading, the surface contains four- and six-coordinated aluminium as well as patches of aluminium hydroxides. Calcination results in two competing process, that is the diffusion of aluminium into the silica network and sintering of aluminium into separate patches of a phase which mainly consists of octahedral Al. These ASAs exhibit Brønsted acidity similar to industrial amorphous silica-aluminas prepared by the grafting of aluminium on very reactive silica gels. Their acidity does not vary systematically with the aluminium concentration, except below 5 wt% Al 2O 3. The acidity increases with the calcination temperature. The active sites form due to the diffusion of aluminium into the silica network at high temperatures, leading to Al substitutions of Si atoms. This is expected as the acidity does not correlate with anything else, viz., the amount of four-coordinated aluminium nor the presence of segregated Al or five-coordinated aluminium at the interface of these domains and the mixed silica-alumina phase. The surface of an amorphous silica-alumina consists of isolated aluminium grafted onto the silica surface (pure silica-alumina phase) with a very small amount of aluminium in the silica network, which brings about the Brønsted acidity, and small patches of aluminium oxides.

Hydrogen production by low-temperature reforming of organic compounds in bio-oil over a CNT-promoting Ni catalyst

Present study reports on high catalytic activity of CNTs-supported Ni catalyst ( x% Ni-CNTs) synthesized by the homogeneous deposition–precipitation method, which was successfully applied for low-temperature reforming of organic compounds in bio-oil. The optimal Ni-loading content was about 15 wt%. The H 2 yield over the 15 wt% Ni-CNTs catalyst reached about 92.5% at 550 °C. The influences of the reforming temperature ( T), the molar ratio of steam to carbon fed (S /C) and the current ( I) passing through the catalyst, on the reforming process of the bio-oil over the Ni-CNTs' catalysts were investigated using the stream as the carrier gas in the reforming reactor. The features of the Ni-CNTs' catalysts with different loading contents of Ni were investigated via XRD, XPS, TEM, ICP/AES, H 2-TPD and the N 2 adsorption–desorption isotherms. From these analyses, it was found that the uniform and narrow distribution with smaller Ni particle size as well as higher Ni dispersion was realized for the CNTs-supported Ni catalyst, leading to excellent low-temperature reforming of oxygenated organic compounds in bio-oil.

Oxidation of Benzyl Alcohol to Benzaldehyde by tert-Butyl Hydroperoxide over Nanogold Supported on TiO2 and other Transition and Rare-Earth Metal Oxides

Liquid-phase oxidation of benzyl alcohol to benzaldehyde by tertiary butyl hydroperoxide (at 95 °C) over nanogold supported on TiO2 and other transition-metal oxides (viz, MnO2, Fe2O3, CoOx, NiO, CuO, ZnO, and ZrO2) or rare-earth oxides (viz, La2O3, Sm2O3, Eu2O3, and Yb2O3) by the homogeneous deposition−precipitation (HDP) method has been investigated. The Au/TiO2 catalyst, prepared using the HDP method, showed high activity and selectivity in the reaction. The ZrO2-supported nanogold catalyst (HDP) also showed very good performance. The Au/TiO2 catalyst that was prepared using the deposition−precipitation (DP) method, however, showed poor catalytic activity, mostly because of its much-lower gold loading and/or lower Au3+/Au0 ratio. Irrespective of the catalyst preparation method, the catalytic activity increased as the gold loading increased. The gold deposition method strongly influenced the amount of gold that was deposited on TiO2, the gold particle size distribution, and also the surface Au3+/Au0 rat...

Supported Nano-Gold Catalysts for Epoxidation of Styrene and Oxidation of Benzyl Alcohol to Benzaldehyde

Nano-gold particles supported on different alkaline earth oxides (viz. MgO, CaO, BaO and SrO), Gr. IIIa metal oxides (viz. Al2O3, Ga2O3, In2O3 and Tl2O3), transition metal oxides (viz. TiO2, Cr2O3, MnO2, Fe2O3, CoOx, NiO, CuO, ZnO, Y2O3 and ZrO2), rare earth metal oxides (viz. La2O3, Ce2O3, Nd2O3, Sm2O3, Eu2O3, Tb2O3, Er2O3 and Yb2O3) and U3O8 [all prepared by depositing gold on corresponding metal oxide support by deposition precipitation (DP) and/or homogeneous deposition precipitation (HDP) method] were evaluated for their catalytic performance in the liquid phase epoxidation of styrene by tert-butyl hydroperoxide (TBHP) to styrene oxide and also in the solvent-free benzyl alcohol-to-benzaldehyde oxidation (by molecular oxygen or TBHP) reactions. For the epoxidation, the catalytic performance (styrene oxide yield) of the most promising nano-gold catalysts prepared by the HDP method was in the following order: Au/MgO > Au/Tl2O3 > Au/Yb2O3 > Au/Tb2O3 > Au/CaO (or TiO2). However, for the oxidation of benzyl alcohol to benzaldehyde by molecular oxygen, the order of choice for the most promising catalysts (based on benzaldehyde yield) was Au/U3O8 > Au/Al2O3 > Au/ZrO2 > Au/MgO. Whereas, when TBHP was used as an oxidizing agent for the benzyl alcohol oxidation, the order of choice for the most promising catalysts was Au/U3O8 > Au/MgO > Au/TiO2 > Au/ZrO2 > Au/Al2O3. The catalytic performance of a particular supported nano-gold catalyst was thus found to depend on the reaction catalysed by them. Moreover, it is strongly influenced by a number of catalyst parameters, such as the metal oxide support, the method of gold depositon on the support, the gold loading and also on the catalyst calcination temperature. Nano-gold particles-support interactions seem to play an important role in controlling the deposition of gold (amount of gold deposited and size and morphology of gold particles), formation of different surface gold species (Au0, Au1+ and Au3+) and electronic properties of gold particles and, consequently, control the catalytic performance (both the activity and selectivity) of the supported nano-gold catalysts in the reactions. The nano-gold catalysts prepared by the HDP method showed much better catalytic performance than those prepared by the DP, coprecipitation or impregnation method; in general, the HDP method provided supported gold catalysts with much higher gold loading and/or smaller size gold particles than that achieved by the DP and other methods.

Magnesium oxide supported nano-gold: A highly active catalyst for solvent-free oxidation of benzyl alcohol to benzaldehyde by TBHP

Nano-size gold particles deposited on MgO by the homogeneous deposition–precipitation showed very high catalytic activity with nearly 100% conversion of benzyl alcohol in a short reaction period (0.5 h) and more over showed excellent reusability in the process. Influence of the catalyst support (MgO, CaO, BaO, SrO, Al2O3, Ga2O3 and In2O3), method of gold deposition, Au loading and catalyst calcination temperature and also that of the reaction conditions (viz. reaction time and temperature) on the benzyl alcohol to benzaldehyde oxidation have been thoroughly investigated.

Oxidation of Carbon Monoxide over a Fibrous Titania-Supported Gold Catalyst

Abstract Fibrous titania with different micro-structures was prepared from a potassium dititanate whisker precursor by ion exchange and thermal treatment. Gold nanoparticles (1%) were deposited on two fibrous titania supports calcined at 600 and 800 °C, respectively, by homogeneous deposition-precipitation. The Au/TiO 2 catalysts were characterized by X-ray diffraction, N 2 adsorption, scanning electron microscopy, transmission electron microscopy, and CO oxidation. The fibrous titania calcined at 600 °C had a mesoporous structure, whereas the meso-structure totally collapsed when calcined at 800 °C. The crystallinity of the fibrous titania support had a high thermal stability, and the anatase phase was maintained even after calcination at 800 °C. The meso-structure of TiO 2 calcined at 600 °C was unchanged after deposition of gold particles. Although the particle size of gold on TiO 2 calcined at 600 °C was much larger than that on TiO 2 calcined at 800 °C, their catalytic performances were comparable.

Performance of carbon nanomaterial (nanotubes and nanofibres) supported platinum and palladium catalysts for the hydrogenation of cinnamaldehyde and of 1-octyne

Within this work, different carbon nanomaterials, multi-walled nanotubes (MW-CNT) as well was herringbone (HB-CNF) and platelet nanofibres (PL-CNF), were synthesised and loaded with the active metal (platinum or palladium) by means of selected functionalisation techniques. As loading methods conventional techniques (wetness impregnation (WI), ion adsorption (IA), homogeneous deposition precipitation (HDP)) as well as a very young method, the colloidal microwave process (CMP), were applied. For comparison, a conventional activated charcoal (Fluka, Norit) was loaded by the CMP. In addition, commercial catalysts such as Pt- and Pd-catalysts on activated charcoal (Fluka) as well as the industrially well-established Lindlar catalyst (Fluka) and a Pt/alumina material (Aldrich) were employed. In order to evaluate the catalytic performance of the materials, two different hydrogenation reactions were carried out. The platinum materials were tested for the hydrogenation of cinnamaldehyde and the palladium catalysts were applied in the hydrogenation of 1-octyne. Regarding the hydrogenation of cinnamaldehyde, the materials produced via the CMP showed the best results in terms of activity and selectivity towards the desired intermediate cinnamyl alcohol in comparison to the commercial materials. It was also shown that not only the functionalisation technique (CMP) but also the support material is crucial concerning catalyst performance. Thus, with the herringbone nanofibre supported Pt-catalyst (CMP) the most promising results were obtained with respect to activity and selectivity. Within the hydrogenation of 1-octyne the CMP-loaded Pt/platelet-nanofibre catalyst showed similar characteristics in activity and selectivity compared to the commercial Lindlar catalyst. However, in long term experiments the nanofibre material featured much higher stability. A commercial Pt/activated charcoal material was most active but least selective towards the favoured intermediate 1-octene. The presented results indicate a strong influence of carbon nanomaterials as a support and of the functionalisation technique on the performance of hydrogenation catalysts.

Insights into the nature of alumina-supported MnOOH and its catalytic performance in the aerobic oxidation of benzyl alcohol

Abstract We report the synthesis of alumina-supported manganese catalysts by a homogeneous deposition–precipitation method and their catalytic application in the aerobic oxidation of benzyl alcohol. Benzyl alcohol conversion of 93% was achieved with benzaldehyde as the main product. This Mn-based catalyst can be recycled up to six times without losing catalytic activity. X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) indicated that MnOOH species are highly dispersed on the alumina surface at low Mn loadings ( 3 O 4 crystallites at high Mn loadings.

Preparation of Cu/SBA-15 catalysts by different methods for the hydrogenolysis of dimethyl maleate to 1,4-butanediol

Cu/SBA-15 catalyst prepared by the homogeneous deposition precipitation (HDP) method shows the highest activity and selectivity in gas phase hydrogenolysis of dimethyl maleate to 1,4-butanediol. The effects of the preparation methods on the textural and structural properties of Cu/SBA-15 catalysts have been systematically investigated. Mesoporous siliceous SBA-15-supported Cu catalysts have been prepared by different methods and systematically characterized. The results revealed that the incipient wetness impregnation (IWI) method gives poor dispersion of copper species, whereas much better dispersion is found in catalysts prepared by the deposition precipitation (DP), grafting, and homogeneous deposition precipitation (HDP) methods. The Cu/SBA-15 catalyst prepared by the grafting method is rich in Cu + , while a partial destruction of the hexagonal mesostructure of SBA-15 occurs in the catalyst prepared by the HDP method. In gas phase hydrogenolysis of dimethyl maleate (DMM) to 1,4-butanediol (BDO), the hydrogenolysis activities of the catalysts follow the sequence of the metallic Cu surface areas; the catalyst prepared by the HDP method exhibits the highest activity and selectivity. Irrespective of the much smaller metallic Cu surface area of the catalyst prepared by the grafting method, this catalyst exhibits only slightly lower activity than that prepared by the DP method, suggesting that Cu + also participates in DMM hydrogenolysis. The reaction conditions are further investigated over the Cu/SBA-15 catalyst prepared by the HDP method, aiming to obtain a high yield of BDO.

Alkaline earth oxide supported nano-gold catalysts: influence of support, preparation method and calcination temperature of catalyst on its gold particle size and morphology

Influence of the metal oxide support, method of gold deposition and calcination temperature on the size and morphology of the nano-size gold particles deposited on alkaline earth metal oxides has been investigated. A number of alkaline earth oxide (viz. Mgo, CaO, SrO or BaO) supported nano-gold catalysts were prepared by depositing gold on the support by the deposition precipitation (DP) and homogeneous deposition precipitation (HDP) methods. The catalysts were calcined at different temperatures (400°C-900°C). The catalysts were characterised for their Au particles (size and morphology) using TEM/HRTEM. The catalytic activity of the supported nano-gold catalysts in the epoxidation of styrene to styrene oxide by tertiary butyl hydroperoxide could be correlated well with the Au loading and/or Au particle size of the catalysts.