Analysis and interpretation of acidic nature of aluminosilicates

Aluminosilicate solid acid catalysts, especially zeolites, have been widely utilized in petroleum refinery and environmentally benign chemical processes. The acidic property of aluminosilicates has been a subject of advanced studies. Recently an ammonia IRMS-TPD (infrared/mass spectroscopy temperature-programmed desorption) method, an application of operando technique, has been developed to quantify the number and strength distribution of each of Brønsted and Lewis sites on a solid. With an aid of quantum chemistry, relationships among the composition, structure and acidic property are being unveiled to totally understand the chemistry of SiOHAl unit in the aluminosilicates

Methods for Calculating Heat of Adsorption from Temperature-Programmed Desorption Spectrum under Equilibrium Control

Methods for calculation of heat of adsorption from a TPD (temperature-programmed desorption) spectrum are reviewed. Ammonia TPD is well analyzed by these methods to clarify the acidic properties of various solid catalysts

Keggin-type molybdovanadophosphoric acids loaded on ZSM-5 zeolite as a bifunctional catalyst for oxidehydration of glycerol

Glycerol is a promising renewable feedstock for the manufacture of C3 derivatives. We investigated the one-pass oxidehydrarion of glycerol through the dehydration of glycerol into acrolein, followed by the oxidation of acrolein. A novel bifunctional catalyst for this reaction was prepared by loading the Keggin-type molybdovanadophosphoric acid H3+xPVxMo12-xO40 (x = 0–3) on ZSM-5 (MFI) zeolite (Si/Al = 45) exhibiting both dehydration and oxidation activity. H5PV2Mo10O40 and H6PV3Mo9O40 were stable and dispersed on ZSM-5 zeolite, and the acidic property of the ZSM-5 zeolite was retained. The oxidehydration of glycerol was catalyzed by H5PV2Mo10O40 loaded on the ZSM-5 zeolite with high selectivity of acrylic acid. In-situ IR analysis suggests that acrolein molecules adsorbed on H5PV2Mo10O40/ZSM-5 were converted into acrylic acid due to the inhibition of side-reactions such as polymerization and auto-condensation, which induced coke formation, compared with the other Mo and V-based oxides loaded on ZSM-5 zeolite

Compensation between activation entropy and enthalpy in reactions of aromatic hydrocarbons catalyzed by solid acids

Reaction rates of toluene disproportionation (A) and cumene cracking (B) normalized by the number of Brønsted acid sites were analyzed on aluminosilicates. The activation entropy showed linear and compensatory relationship against the activation enthalpy. The slope of entropy-enthalpy plot was in the order of (B)>(A)>small alkane cracking, whereas the intercept on the horizontal axis was in the order of propane and isobutane cracking>linear C4–8 alkanes and iso-pentane cracking>(A)>(B). The former is consistent with the bulkiness of reactant, while the latter is consistent with intrinsic difficulty of formation of intermediate cations

Selective dealkylation of alkyl polycyclic aromatic hydrocarbons towards innovative upgrading process of practical heavy oil

The dealkylation of alkyl polycyclic aromatic hydrocarbons (APAHs) in vacuum gas oil (VGO) was studied as a novel upgrading process alternative to conventional processes. A silica-monolayer loaded on alumina (SMA) with weak Brønsted acid sites and large pore size exhibited higher activity than amorphous silica-alumina and zeolites (USY and ZSM-5). The SMA almost completely converted the APAHs into aromatics and alkanes, but a small amount of APAHs with methyl and ethyl groups (short-chain) were unreacted. The larger pore size of the SMA was proposed to be enough for bulky APAHs to diffuse. The dealkylation by the SMA formed large amounts of long-chain alkanes, which can be utilized as light oil and kerosene for fuel, lubricating oil, etc. The cracking of long-chain alkanes did not proceed, and thus scarcely formed lighter alkanes. The SMA in the reaction adsorbed alkanes but did not form coke, and therefore exhibited continuous dealkylation activity. Additionally, it was revealed that the pore size of the SMA slightly affected the composition of the formed alkanes

Enhancement of Catalytic Activity for Toluene Disproportionation by Loading Lewis Acidic Nickel Species on ZSM-5 Zeolite

Impregnation of various heteroelements on the ZSM-5 zeolite was applied to improvement of the catalytic activity in toluene disproportionation. Nickel loaded on ZSM-5 (Ni/ZSM-5) exhibited higher catalytic activity (toluene conversion) and lower benzene / xylene ratio (closer to the stoichiometry, meaning low rate of side reaction) than H-ZSM-5 zeolite. The Ni/ZSM-5 with Ni/Al = 0.6 showed the maximum in catalytic activity, and excess Ni loading caused decrease in the conversion and increase in the benzene / xylene ratio due to decrease of acid amount and acceleration of dealkylation, respectively. The detailed analysis of acidic property by means of ammonia IRMS-TPD method showed that the Ni loading generated Lewis acid sites on the zeolite. The synergy of Brønsted and Lewis acid sites, ascribed to Si-OH-Al and Ni species, respectively, is suggested to give the high activity of desired reaction

Fabrication and catalytic activity of thermally stable gold nanoparticles on ultrastable Y (USY) zeolites

Au was deposited on ultrastable Y (USY) zeolites using an ion-exchange method. Up to 5.5 wt% Au was introduced into the NH4-form of USY zeolites. In contrast, deposition of Au hardly took place on the H- and Na-forms of Y-type zeolites, NH4-forms of mordenite, and ZSM-5. Treatment of the Au-loaded USY zeolite in a H2 atmosphere, afforded Au0 nanoparticles. These particles were thermally stable even at 973 K, where their mean particle diameter was 3.7 nm. In contrast, highly aggregated Au particles were observed after thermal treatment at temperatures lower than 523 K, followed by storage in air for a month. The resulting particle sizes were in good correlation with the IR band intensity of the adsorbed CO and the catalytic activity of Au in the aerobic oxidation of benzyl alcohol. The Au nanoparticles showed highest activity when the Au/USY zeolite was thermally treated at 673–973 K. A negligible deactivation was observed after repeating the reaction at least 12 times. In the case of Au/TiO2 catalyst prepared by the deposition-precipitation method, the highest activity was observed at 573 K, which was lower than the temperature used for the Au/USY zeolites. This study demonstrated the potential use of the NH4-form of USY zeolites for supporting Au

One-Step Conversion of Glutamic Acid into 2-Pyrrolidone on a Supported Ru Catalyst in a Hydrogen Atmosphere: Remarkable Effect of CO Activation

Glutamic acid, an abundant nonessential amino acid, was converted into 2-pyrrolidone in the presence of a supported Ru catalyst under a pressurized hydrogen atmosphere. This reaction pathway proceeded through the dehydration of glutamic acid into pyroglutamic acid, subsequent hydrogenation, and the dehydrogenation–decarbonylation of pyroglutaminol into 2-pyrrolidone. In the conversion of pyroglutaminol, Ru/Al2O3 exhibited notably higher activity than supported Pt, Pd, and Rh catalysts. IR analysis revealed that Ru can hydrogenate the formed CO through dehydrogenation–decarbonylation of hydroxymethyl groups in pyroglutaminol and can also easily desorb CH4 from the active sites on Ru. Furthermore, Ru/Al2O3 showed the highest catalytic activity among the tested catalysts in the conversion of pyroglutamic acid. Consequently, the conversion of glutamic acid produced a high yield of 2-pyrrolidone by using the supported Ru catalyst. This is the first report of this one-pot reaction under mild reaction conditions (433 K, 2 MPa H2)„ which avoids the degradation of unstable amino acids above 473 K

Acidic Property of BEA Zeolite Synthesized by Seed-directed Method

The acidic property of a BEA zeolite prepared by a seed-directed synthesis (SDS) method without organic structure directing agent (OSDA) was analyzed by a method of ammonia infrared / mass spectroscopic (IRMS) temperature-programmed desorption (TPD). The number of Brønsted acid sites on the SDS-BEA zeolite was larger than that on a conventional BEA zeolite synthesized from using OSDA. The enthalpy of ammonia desorption, distributed mainly in a range between 115 and 145 kJ mol-1, was in agreement with the acid strength region generated by isomorphous substitution of Si4+ by Al3+ in the BEA framework. These observations confirm that the microstructure around the incorporated Al in the SDS-BEA zeolite was equivalent to that in the conventional one

Assignments of Bending Vibrations of Ammonia Adsorbed on Solid Surfaces

Bending vibrations in the infrared (IR) spectra of ammonia adsorbed on Lewis acidic metal oxides, i.e., Al2O3, ZrO2 and TiO2, and zeolite were analyzed with an aid of density functional theory (DFT) calculations. The results by DFT methods reveal the wavenumbers of the vibration modes (ν4 and ν2) of NH4 bonded to Brønsted acid site and the vibration modes (δs and δd) of NH3 species coordinated to a Lewis acidic metal center (M = Al, Zr or Ti). The wavenumbers calculated based on DFT were reasonably in agreement with the experimentally observed values. The estimation of wavenumbers suggests that the δs vibration of NH3 hydrogen-bonded is invisible on a zeolite, because it is hidden by an intense absorption due to skeletal vibration. On the other hand, multiple bands of asymmetric bending modes (δd and ν2) observed on a zeolite were assigned. A quantification method of Brønsted and Lewis acid sites, and hydrogen-bonded NH3 is provided based on the peak assignments