Conventional Incipient Wetness Impregnation Research Articles

Synthesis of biodiesel from sunflower oil with silica‐supported NaOH catalysts

AbstractBACKGROUND: A series of NaOH catalysts supported on commercial silica have been prepared by conventional incipient wetness impregnation and their activity tested in the reaction of transesterification of refined sunflower oil with methanol at 323 K and atmospheric pressure. The effects of the molar methanol/oil ratio, catalyst concentration, NaOH loading and calcination of the supported catalysts have been investigated.RESULTS: It has been found that the transesterification rate largely depends on the catalyst/methanol ratio and that calcination of the NaOH catalysts supported on silica, even at moderate temperatures, had a very negative effect on their activity. Selectivity, on the other hand, is more affected by the methanol/oil ratio. Selectivity for methyl esters (biodiesel) improved with the methanol/oil ratio due to an increased transesterification rate of diglycerides, whereas the selectivity for monoglycerides was not affected.CONCLUSION: The NaOH/silica catalysts suffered from a significant lack of chemical stability under reaction conditions as evidenced by measurements of sodium extracted during the reaction progress; therefore, their performance was affected by the presence of Na dissolved in the methanol phase. Copyright © 2008 Society of Chemical Industry

Ni catalysts for sorption enhanced steam methane reforming

Sorption enhanced steam methane reforming (SESMR) is a process for H2 production at low temperatures. The process requires an active and stable catalyst. For this purpose, a series of hydrotalcite-like catalysts (HT) with different Ni loadings have been prepared by a co-precipitation technique and compared with catalysts prepared by conventional incipient wetness impregnation. The co-precipitation route resulted in a stronger interaction between the support and nickel than the incipient wetness route. As a result, smaller Ni crystals with excellent stability and high activity for steam reforming of methane were obtained, even at high loadings. 40 wt% Ni/HT was found to be the most promising candidate for application in SESMR.

Ag/SiO 2 catalysts prepared via γ-ray irradiation and their catalytic activities in CO oxidation

We explored the synthesis of Ag/SiO 2 catalysts via γ-ray irradiation at room temperature. AgNO 3/SiO 2 prepared by the conventional incipient wetness impregnation method was employed as the precursor. Ag/SiO 2 catalyst prepared by calcining AgNO 3/SiO 2 at 500 °C was also prepared for comparison. The Ag/SiO 2 catalysts were characterized with X-ray diffraction, X-ray photoelectron spectroscopy, and diffuse reflectance UV–vis spectrum, and their catalytic activities towards CO oxidation were also tested. γ-Ray irradiation successfully reduced Ag + anchored on SiO 2 into silver nanoparticles at room temperature. Existence of excess water during the γ-ray irradiation led to the formation of larger silver nanoparticles. These catalysts behaved differently in CO catalytic oxidation. Compared with Ag/SiO 2 prepared by calcination that showed a certain low temperature catalytic activity but poor stability, Ag/SiO 2 prepared by room temperature γ-ray irradiation showed an inferior low temperature catalytic activity and a better stability. The different catalytic behavior is associated with the various crystalline sizes of silver nanoparticles in Ag/SiO 2 prepared by different methods.

Synthesis of nanodispersed oxides of vanadium, titanium, molybdenum, and tungsten on mesoporous silica using atomic layer deposition

The advantages of the atomic layer deposition (ALD) method for preparation of tungsten, vanadium, titanium, and molybdenum oxide catalyst supported on mesoporous silica are discussed, with emphasis on the importance of synthesis conditions on dispersion, structure and activity of the resulting materials. A suite of complementary techniques such as DRS-UV/Vis, BET, 1H-NMR, XRD, and TEM were used to study the structural properties of the supported metal oxides, and probe reactions such as 2-butanol dehydration and ethanol partial oxidation were used to demonstrate the potential advantages of the ALD-prepared catalysts. Specifically, highly dispersed oxides of titanium, molybdenum, and tungsten oxide on mesoporous silica were synthesized using the ALD method. It is also demonstrated that attainment of high dispersions of vanadium oxide on mesoporous silica requires the presence of at least a single layer of titanium oxide due to the well-known poor interaction between vanadia and silica. The highly dispersed catalysts prepared here by ALD methods exhibited superior catalytic performance relative to those prepared using conventional incipient wetness impregnation.

Thermolytic molecular precursor route to site-isolated vanadia–silica materials and their catalytic performance in methane selective oxidation

The thermolytic molecular precursor (TMP) method was used to prepare site-isolated, high-surface area vanadia–silica (V/SBA15) materials of various V loadings via the grafting of two precursors, OV[OSi(O t Bu) 3] 3 ( 1) and OV(O t Bu) 3 ( 2). Spectroscopic analysis indicates that excellent synthetic control was established for the exclusive formation of a pseudotetrahedral monovanadate (VO 4) structure on all catalyst surfaces. Another V/SBA15 catalyst was prepared via conventional incipient wetness impregnation (WI) with aqueous NH 4VO 3. A spectroscopic investigation of this catalyst revealed the presence of monovanadate and polyvanadate species along with small domains of V 2O 5. The TMP materials behave as single-site catalysts in the selective oxidation of methane to formaldehyde up to a V coverage of 0.47 V nm −2 and demonstrate superior activity compared with the WI catalyst. A space–time yield of 5.84 kg CH 2O kg −1 cat h −1 was observed, more than twice the highest value previously reported.

The influence of the preparation method and the Co loading on the structure and activity of cobalt oxide/ γ-alumina catalysts for NO reduction by propene

In the present work we studied the influence of the preparation method and the Co loading on the physicochemical properties and the catalytic activity of the cobalt oxide/ γ-alumina catalysts for the reduction of NO by propene under net oxidizing conditions. Two series of catalysts containing 1 and 5% w/w Co, respectively, were prepared using three preparation methods, namely, the equilibrium deposition filtration (EDF), the conventional incipient wetness impregnation (IWI) and the IWI adding nitrilotriacetic acid (nta) in the impregnating solution (IWInta). The catalysts were tested at various temperatures in the range 300–550 °C using a fixed-bed microreactor for the NO reduction by propene under lean burn conditions. The evolution of the Co species on the alumina surface was followed after each preparation step by diffuse reflectance spectroscopy (DRS). It was found that the catalysts of the first series were more active for the title reaction than those of the second one. The EDF sample of the first series was proved to be the most active and selective one followed by the IWI and then the IWInta sample of the same series. The DRS results indicated that the enhanced activity and selectivity of the EDF sample could be attributed to the increased concentration of isolated Co(II) inner sphere complexes of octahedral coordination, which are formed on the support surface by adsorption of the corresponding aqueous complexes, [Co(H 2O) 6] 2+, being in the impregnating solution. These inner sphere complexes are transformed upon thermal treatment into a CoAl 2O 4 like phase with high dispersion. On the other hand, the [Co(H 2O) 6] 2+(NO 3) 2− and [ Co - nta ] − ⋅ NH 4 + (or H +) and/or [ Co - 2nta ] 4 + ⋅ 4 NH 4 + (or 4H +) complex salts, precipitated on the alumina surface upon drying in the cases of the IWI and IWInta samples, are transformed upon calcination into CoAl 2O 4 like phases with lower dispersion. All the samples of the second series promoted the propene combustion as well as the oxidation of NO and N 2, used as carrier gas, to NO 2. DRS results revealed that in all these samples cobalt(III) oxo species are formed in addition to the CoAl 2O 4 phase. These species are considered to be responsible for the enhancement of the rates of the oxidation reactions mentioned above.

Synthesis of novel core-shell structured WO 3/TiO 2 spheroids and its application in the catalytic oxidation of cyclopentene to glutaraldehyde by aqueous H 2O 2

Novel core-shell structured WO 3/TiO 2 spheroids were synthesized through a conventional incipient wetness impregnation method and systematically characterized by X-ray diffraction, N 2 sorption, scanning electron microscopy, transmission electron microscopy, laser Raman spectroscopy, thermogravimetric and differential thermal analysis, X-ray photoelectron spectroscopy, and NH 3 temperature-programmed desorption. It was found that tungsten species are highly dispersed in the interlayer between the core and the shell layer of the TiO 2 support and that there are interactions between the tungsten species and the TiO 2 support that could provide abundant oxygen defect lattice. It is also found that the as-prepared WO 3/TiO 2 material is highly active as a catalyst for the selective oxidation of cyclopentene to glutaraldehyde with aqueous hydrogen peroxide as the green oxidant. Proper content and high dispersion of tungsten species, the interaction between the tungsten species and the support, as well as the medium strong acidity of the novel WO 3/TiO 2 catalyst all account for this material's high activity.

Photocatalytic evolution of hydrogen over mesoporous [formula omitted] supported NiO photocatalyst prepared by single-step sol–gel process with surfactant template

Photocatalytic activity of mesoporous titania supported nickel oxide photocatalyst synthesized by single-step sol–gel (SSSG) process combined with surfactant-assisted template method was investigated for hydrogen evolution from an aqueous methanol solution, in comparison with one prepared by conventional incipient wetness impregnation (IWI) method. In single-step sol–gel process, nickel precursor was introduced into the titania sol prepared with the aid of a surfactant template behaving as pore-controlling agent to attain meso-scaled pore. The single-step sol–gel photocatalyst was experimentally found to enhance the photocatalytic evolution of hydrogen rather than the impregnated one. The optimum level of nickel loading in photocatalytic activity test for single-step sol–gel method was slightly higher than that for incipient wetness impregnation method. Characterization results demonstrated the significant modification of physical characteristics of the single-step sol–gel photocatalyst, anticipated to relating to the observation of higher photocatalytic hydrogen evolution activity.

A new charge alternating model of localization of bivalent cations in high silica zeolites with distantly placed aluminum atoms in the framework

The present communication reports an unexpected result on quantitative substitution in HZSM-5 of all acidic protons by bivalent zinc cations via chemical reaction with zinc vapor at 800 K. Based on this result we suggest a new model for localization of bivalent cations in high silica zeolites with distantly placed aluminum atoms in the framework. According to this model some of the bivalent cations can be localized at the isolated singly negatively charged aluminum occupied oxygen tetrahedra. In parallel the equivalent number of the isolated framework aluminum atoms remains without compensating protons or zinc cations. Their negative charges are compensated indirectly by coulomb interaction with the surrounding excessively charged cationic sites. The resulting Lewis sites with only partially compensated positive electric charges possess unusually high chemical activity. They very strongly perturb molecular hydrogen at 77 K and dissociatively adsorb it at temperatures only slightly above room temperature. Application of low temperature H 2 adsorption as a molecular probe enables us to distinguish such unusual sites from Zn 2+ cations at the conventional ion exchange positions. The similar unusual Lewis sites distantly separated from basic oxygen have also been previously detected by low temperature hydrogen adsorption in the samples prepared by conventional incipient wetness impregnation of HZSM-5 with aqueous solution of zinc nitrate though in smaller amount.

A biomass-supported Na2CO3 sorbent for flue gas desulfurization.

A novel sorbent for SO2 removal has been investigated. The sorbent is obtained by conventional incipient wetness impregnation of abandoned biomaterials (straw or dried leaves) with an aqueous solution of Na2CO3. A material with the composition 80 wt % Na2CO3/straw shows a desulfurization activity which is both higher and faster than that of the reference sample Na2CO3/gamma-Al2O3. The breakthrough and stoichiometric SO2 adsorption efficiencies for 80 wt % Na2CO3/straw reach 48.9% and 80.6%, respectively, at a temperature of 80 degrees C. The adsorption efficiencies are almost constant in the temperature range 70 to 300 degrees C. According to IR and XPS analysis the main products observed on the spent sorbent are sulfite below 150 degrees C and sulfate at 300 degrees C. The Na2CO3 in 80 wt % Na2CO3/straw can potentially be recycled by the oxidation of the straw with concomitant reduction of the sulfite species to elemental sulfur, making the proposed process CO2 neutral.

Calorimetric measurements of the acidity of supported vanadium oxides prepared by ALE and impregnation

The surface acidic properties of supported vanadium oxide catalysts prepared by atomic layer epitaxy (ALE) and for comparison by a conventional incipient wetness impregnation were investigated by adsorption microcalorimetry, using ammonia as probe molecule. The acidic characteristics were strongly affected by the preparation method and the oxide supports. When using γ-Al 2O 3 and TiO 2 as supports, the acidic character of supported vanadium catalysts always decreased compared to vanadia-free supports, whereas on weakly acidic SiO 2, new acidic centres were created when depositing V 2O 5. The same types of acidic sites, Lewis and Brönsted, were present in all the catalysts, but those prepared by ALE showed stronger acidity. The ALE samples were more easily reduced by H 2 thermo-programmed reduction and were twice as active as the impregnated samples in propane dehydrogenation to propene.

Infrared Spectroscopic Characterization of Sulfide Cluster-Derived Ensembles

ABSTRACTThe transition metal sulfide clusters (MeCp)2Mo2(μ-SH)2(μ-S)2, (MeCp)2Mo2Co2(μ3-S)2(μ4-S)(CO)4 [MoCoS], and (MeCp)2Mo2 Fe2 (μ3-S)2(CO)8, (MeCp = methylcyclopentadienyl) were used to prepare γ-Al2O3-supported catalysts. For comparison, a series of supported materials was also prepared using conventional incipient wetness impregnation. Infrared spectroscopy of adsorbed species was used to characterize the sites in the clusterderived and conventionally prepared catalysts. Nitric oxide chemisorbed onto the MoCoS/A catalyst was associated initially only with Co sites and then upon gentle heating shifted to the Mo sites, indicating that Co and Mo were in close proximity. In contrast, NO adsorbed onto both Co and Mo sites in the conventionally prepared materials and desorbed independently from these two types of sites. Infrared spectra of adsorbed thiophene and pyridine were similar for the clusterderived and conventionally prepared catalysts. Thiophene reacted at 100 °C to produce both olefinic species. The most abundant products from thiophene HDS were 1-butene, cis-2-butene, and trans-2-butene. Displacement studies showed that thiophene, pyridine, and NO adsorbed to the same site. The most active sites for HDS and HDN contained both Mo and a late transition metal. The HDN product distributions suggested that Mo was selective for C=N bond cleavage while the late transition metals were more active for C=C hydrogenolysis.