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Understanding the effects of synthetic parameters in the catalytic activity of heterogeneous catalysts is of utmost importance when aiming for optimal reaction conditions. Hence, we disclose in this work the synthesis and characterization of cerium-modified MCM-41 materials. In addition, it was observed for the first time, differences in catalytic activity when using different cerium synthetic precursors: CeCl3&middot, 7H2O and Ce(NO3)3&middot, 6H2O (Ce-MCM-Cl and Ce-MCM-NO3, respectively). A mechanism for cerium incorporation in MCM-41 was proposed, where [Ce(OH)3] species were hydrogen bonded to silicate anions, forming framework Ce-O-Si bonds during condensation and, consequently, causing distortion of the typical hexagonal mesophase. It was also observed that Ce(OH)3 formed aggregated layers with template assemblies during synthesis, resulting in non-framework CeO2 species on the MCM-41 surface after calcination. These CeO2 species were preferentially formed for Ce-MCM-NO3 and were attributed to the nitrate ions&rsquo, strong binding to template molecules. In the solvent free liquid-phase oxidation of benzyl alcohol (BzOH), Ce-MCM-Cl achieved better BzOH conversions and benzaldehyde (BzD) yields, while Ce-MCM-NO3 offered increased BzD selectivity. The catalysts&rsquo, reusability was also studied over three catalytic runs, where Ce-MCM-NO3 was more resistant than Ce-MCM-Cl towards deactivation. The observed catalytic behavior shows the importance of metal precursors in the obtainment of materials with desirable final properties.

Zeolite Y was dealuminated in the solid-state at several degrees (5, 10, 15 and 20%) using (NH 4 ) 2 SiF 6 as dealumination agent. The materials were heated to 80, 100, 120, 140, 160, 180 and 200 °C to investigate the best temperature at which the samples retain their crystallinity and acidity. The solids obtained were characterized by XRD, FTIR, TG/DTG, XRF, 27 Al and 29 Si MAS NMR and N 2 physisorption. They were also subjected to pyridine adsorption and calorimetric experiments. Structural and textural results showed that lower temperatures (80 and 100 °C) and smaller degrees of dealumination (5 and 10%) maintained the zeolite crystallinity and increased its specific surface area, microporosity and mesoporosity. The study of the materials acidity indicated the presence of Bronsted acid sites with different strength, hydrogen bonding sites and Lewis sites originated from acid leaching. The calorimetric measurements showed higher enthalpy values for some of the dealuminated materials than for the parent zeolite. It also evidenced an increase for the number of acid sites between −160 and −140 kJ mol −1 and a reduction for the other sites, between −140 and −80 kJ mol −1 .

The dealumination of zeolites has been studied to tune acidity, resulting in enhanced catalytic efficiency. MOR, FER, and ZSM-5 were dealuminated to remove 5, 10, 15, or 20 mol% of Al with (NH4)2SiF6 (solid-state reaction at 80 °C). XRD, SEM, and FT-IR showed structural maintenance. Aluminum removal was confirmed by the total Si/Al ratio (XRF and AAS) and 27Al MAS NMR. The dealuminated samples were tested in the dehydration of different alcohols and compared to the protonic parent zeolites. Dealuminated MOR samples exhibited a decrease in coke formation (maximum decrease of 18.3%, 18.2%, and 6.1% for methanol, ethanol, and 1-propanol dehydration, respectively), and an increase in conversion values (maximum increase of 29.0%, 13.9%, and 6.2% for methanol, ethanol, and 1-propanol dehydration). H-FER/20% showed an improvement in methanol (19.9%) and ethanol (3.8%) conversions and a reduction of coke (decrease of 8.6% and 5.6%, respectively), corroborating the highest value of acid sites (0.73 mmol g−1). All catalysts showed 100% selectivity to each desired product. The mechanisms for all dehydrations were related to the presence of Bronsted acid sites. Methanol dehydration might involve the generation of methoxonion ion, and ethoxy groups might be formed for ethanol conversion. For ZSM-5, Lewis acid sites may also participate in the elimination mechanism. High reaction temperature (300 °C) favored intramolecular dehydration to ethylene, avoiding formation of diethyl ether and oligomers. Structural defects on H-ZSM-5/15% could facilitate the access of 1-propanol to active sites, leading to the best combination of TON (0.67), conversion (100%), and coke formation (0.35%).

A task-specific ionic liquid with a Bronsted acid (1-(3-sulfopropyl)-3-methylimidazolium hydrogen sulfate, namely MSI ) bearing an anionic heteropolyacid derivative ([PW 12 O 40 ] 3− , namely PW ) were used as an efficient catalyst for the three-component Mannich and Hantzsch reactions. Using ( MSI ) 3 PW as the catalyst supported in imidazolium-based ionic liquids allowed these multicomponent reactions to take place in good to excellent yields. The Mannich reaction, performed at room temperature, was also evaluated by means of electrospray (tandem) mass spectrometry—ESI-MS(/MS). ESI-MS data pointed to the origin of the ionic liquid effect, i.e., formation of ion pairs with the charged reaction intermediates and furthers association into larger supramolecular aggregates. DFT calculations revealed the strength of the supramolecular interactions between the charged species detected by ESI-MS and the spontaneity association of these ion pairs affording larger supramolecular aggregates.

In this work, activities of HUSY and Ce/HUSY zeolites were studied in transesterification cycles of soybean oil and ethanol to produce biodiesel. The characterization of the materials was performed by FT-IR, XRD, BET method and pyridine adsorption followed by thermal analyses. TG/DTG results indicated a decrease of acid sites for both samples after each reaction cycle. However, Ce/HUSY zeolite showed a superior stabilization of acidic sites after three catalytic cycles and intermediary activation procedures. Biodiesel production exhibited high conversion levels (>96%) for both zeolites in all transesterification cycles. Surface area and pore volume measurements evidenced that cerium incorporation reduced the number of acid sites by interacting with OH groups in the micropore and external area of the zeolitic surface. This interaction resulted in an acid and structural stability, which provided a better activity (99%) than HUSY (96%). The higher conversion values obtained by zeolites showed a final product with a different distribution when compared with the traditional transesterification process. The identification of free fatty acids, diethyl and glycerol ethers in the final products and the reduction of unsaturated compounds indicated that parallel reactions also occurred in the studied systems. Nonetheless, the biofuel produced showed high ester content and did not present changes in its calorific power.

Supported heteropolyacids (HPAs) have been used as catalysts by fine-tuning their heterogenous and Bronsted acidic properties. In this work, supported H 3 PW 12 O 40 (HPW) on MCM-41 was prepared (2–40 wt%) and applied in the intramolecular cyclization of (+)-citronellal. The synthesized materials were characterized by 31 P MAS NMR, XRD, FTIR, pyridine gaseous adsorption, low temperature nitrogen adsorption and thermal analysis. The impregnation of 20% HPW on the surface of MCM-41 decreased the characteristic crystallographic reflections of the support, suggesting that HPW modifies the long-range order. The results show that the HPW was deposited preferentially inside the mesopores of the support and affected the acid strength of the supported catalyst. FTIR studies of pyridine adsorption confirmed the presence of Bronsted and hydrogen bonded acid sites. All synthesized materials were active in the cyclization reaction, but the 20%HPW/MCM-41 sample was the most active. This catalyst showed about 96% conversion and 65% selectivity to the most important stereoisomer (−)-isopulegol, under 1 h reaction. This catalyst was reused four times with a fair degree of deactivation. The decreased activity was attributed to the formation of small agglomerates in the channels of MCM-41.

Zeolites have occupied a distinguished position due to their unique properties as solid acids and catalytic results achieved in several industrial reactions. This work studied the influence of supported WO 3 on USY zeolite structure, acidity and activity towards an esterification reaction. High dispersion of WO 3 species on USY was achieved, but at higher loading (⩾11.4%), microcrystalites of WO 3 were detected below the theoretical monolayer coverage (∼32%). Tungsten species were deposited preferentially inside the zeolite structure and interacted with the Bronsted sites of USY as well as on silanol surface groups with the formation of small aggregates. In addition, dealumination took place, especially in the samples with high WO 3 loading. USY had the most and the strongest acidic sites (Bronsted type), but the incorporation of WO 3 decreased the amount and the strength of the new sites. However, all WO 3 /USY catalysts were more active than USY in the esterification of oleic acid with ethanol (conversion above 74%, 2 h at 200 °C). The calculation of the TOF for a 1 h reaction demonstrated that 11.4% WO 3 /USY was the most active catalyst. Furthermore, it had the lowest rate of deactivation of acid sites after the reaction (∼13% after four cycles). The better performance of the 11.4% WO 3 /USY sample was also attributed to a better distribution of strength of the acidic sites and a more hydrophobic character of the synthesized material.

The surface acidity of the molecular sieve Si-MCM-41 was investigated by liquid phase calorimetric-adsorption analysis (Cal-Ad), gas adsorption measurements (TG-TPD) and infrared spectroscopy using pyridine as the probe molecule. The results showed that Si-MCM-41 evacuated at 200 °C had one type of hydrogen bonding site (n1 = 2.27 mmol g−1 with ΔH1 = −95.3 kJ mol−1) that was much stronger than those in silica gel. These sites corresponded to the total OH groups of the material surface and were able to retain pyridine at higher temperatures than silica gel (400–600 °C). In addition, the material had a higher entropy value (ΔS1 = −250 J K−1 mol−1) than silica gel. This indicates that pyridine is more strongly adsorbed on the surface of Si-MCM-41 than silica-gel, which leads to better catalyst properties. Solid-state 29Si MAS-NMR measurements showed a high amount of silanol groups (52%) in the Si-MCM-41 structure (for the Q2 and Q3 species). These results suggest a highly polar environment caused by the hydroxyl groups that line the walls of the hexagonal long-range ordered pores.

Mixed salts of cesium and ammonium derivatives of H3PW12O40 ((NH4)xCsyH0.5PW) were synthesized by a precipitation/ion exchange method with a different addition order for each cation. The produced salts were characterized by FTIR, XRD, 31P MAS NMR, SEM, pore size and the BET method. FTIR demonstrated that the materials maintained the Keggin structure under all tested conditions. BET results showed that salts formed by proton substitution from ammonium to cesium had much higher surface areas. Characterization by 31P MAS NMR and XRD, demonstrated that the salt structures varied sharply with the degree of hydration. After calcination, the materials were confirmed to have characteristics of solid solutions with random distribution of the cations with similar crystallographic patterns. The primary nanocrystals aggregated to form solids with mesoporous and microporous structures, created by partial unidirectional growth of the nanocrystals during formation of the bigger, round microcrystallites about 0.3–1 μm in size.

Catalysts of H3PW12O40 (H3PW) supported on Nb2O5 were prepared with a wide range of loadings (20–60 wt%) and characterized by FTIR, FT-Raman, XRD, 31P MAS NMR, the BET method and pyridine adsorption in the gas phase. In addition, the acidity was measured by the Cal-Ad method, which combines microcalorimetry and adsorption of pyridine on the solid samples in cyclohexane slurry. Preparation of the catalysts involved two procedures: impregnation in aqueous acid or acetonitrile solutions with further calcination at 200 °C for 8 h. No decomposition of H3PW was observed under these conditions. The results indicated the formation of well-dispersed H3PW species on materials with loadings up to 30 wt%, prepared preferentially in aqueous acid solution. A strong interaction between the heteropolyacid and niobia surface was observed forming species such as [ NbOH 2 ] n + [ H 3 - n PW 12 O 40 ] n - 3 . The H3PW/Nb2O5 materials containing 20–40 wt% presented type II isotherms and showed that surface area, pore volume and pore size decreased as the amount of H3PW increased, whereas the micropore area increased with H3PW loading. According to gaseous pyridine adsorption results, the catalysts presented only Bronsted sites. Microcalorimetric titration demonstrated that the 25 wt% material was the most acidic. The Cal-Ad method provided the enthalpy and number of sites for the strongest interaction with pyridine as: ΔH1 = −119.7 kJ mol−1 and n1 = 0.086 mmol g−1. About 33% of the protons were available for 25% H3PW/Nb2O5, in comparison to only 8% for pure H3PW. A considerable increase in the surface protons was achieved by H3PW on niobia surface.

Esterification of organic acids with alcohols produces an industrially important class of substances with a variety of applications. This work presents an impregnation route to support H3PW12O40 (H3PW) on zirconia (ZrO2) in acidic aqueous solution (HCl 0.1 mol L−1) at different ratios (5, 10, 15, 20, 25, 40 and 60 wt%), which were further applied in the esterification of oleic acid with ethanol. Impregnated samples calcined at 200 °C for 4 h were characterized by FTIR, FT-Raman, XRD, 31P MAS NMR and BET surface area. No decomposition of the Keggin anion structure was observed under these conditions. The XRD results, surface area determination and catalytic tests pointed out that H3PW was well dispersed over the support and only a monoclinic phase of the commercial ZrO2 was detected. An optimum reaction performance (88% of oleic acid conversion) was achieved at 20 wt% loading, 100 °C, 4 h reaction and 1:6 (acid:ethanol) molar ratio. A small leaching of 8 wt% of the initial mass of this catalyst (i.e., the actual loading was 18.4 wt%) was also observed at the end of reaction, which affects the reaction kinetics. Thermal stability studies of 20%H3PW/ZrO2 catalyst, determined by 31P MAS NMR, XRD and FT-Raman revealed that Keggin anion decomposition begins at ca. 500 °C, which was confirmed by the respective decrease of the catalytic activity. A preliminary study of recyclability indicated that a treatment of the spent catalyst involving a sequence of washing with n-hexane, drying at 100 °C and calcining at 300 °C for 4 h, recovered conversion values as high as 70%.

This article reports the synthesis, characterization and application of cerium(III) trisdodecylsulfate trihydrate (Ce[OSO3C12H25]3·3H2O) as a Lewis acid-surfactant-combined catalyst for the production of alkyl esters by solvent-free transesterification and esterification reactions. The new material presents a bilayer lamellar arrangement with an interplanar spacing of d001 = 3.76 nm, and the dodecylsulfate headgroup in a C2v symmetry. The reaction of soybean oil and oleic acid with light alcohols (methanol and ethanol) was used as model reactions and high catalytic activity (TOF = 57.4 mol h−1 molcat−1) was observed. The catalyst converted the used feedstocks to esters in less than 4 h with yields greater than 95%. In addition, it can be used to produce biofuels from unrefined and waste oils in which both triacylglyceride and free fatty acid molecules are present. After reaction, the recovered catalyst maintained its activity (≥95%) for three cycles. The catalyst was characterized by elemental analysis, X-ray powder diffraction (XRD), thermal analysis (thermogravimetry (TG)/derivative thermogravimetry (DTG)/differential thermal analysis (DTA)), pyridine adsorption, and spectroscopic analysis (FTIR and NMR).

Metalloporphyrin catalysts are able to carry out selective oxidation of organic substrates with several oxidizing agents. Recently, mesoporous materials have been studied as supports because they present high specific surface area, better dispersion and regeneration properties. This work presents the results of synthesis, characterization and application of three metalloporphyrin catalysts (FeTPPCl, MnTPPCl and CoTPP, where TPP = tetraphenylporphyrin) anchored on MCM-41, in the reaction of cyclohexene oxidation with hydrogen peroxide. A modified sol–gel preparation was chosen for the synthesis of the MCM-41 mesoporous material, as well as the anchoring was followed by Soxhlet extraction to ensure strong adsorption of the complex. The supported materials were much more stable than pure metalloporphyrins. The synthesized catalysts were characterized by UV–vis, FTIR, XRD, ICP-AES, 29 Si MAS-NMR and thermal analysis, before and after incorporation. Evidence of the metalloporphyrin immobilization was confirmed by elemental analysis and their activity in the oxidation reaction. FeTPPCl/MCM-41 showed higher conversion than CoTPP/MCM-41 and MnTPPCl/MCM-41. However, MnTPPCl/MCM-41 even in low concentration on the support showed a good conversion for the direct oxidation of cyclohexene with the highest turnover number (1.54 × 10 5 ). All catalysts showed similar selectivity that favors allylic oxidation products over epoxidation. No leaching of the metalloporphyrins was observed after the reaction.

Incorporation of niobium into microporous molecular sieves brings up new properties for these materials. ZSM-5 supported catalysts containing 2, 5, 13 and 19 wt.% of niobium pentoxide were prepared by aqueous impregnation and characterized by the combination of thermal (TG/DTA) and spectroscopic methods such as FTIR, FT-Raman, DRIFTS, and 29 Si and 27 Al MAS and 29 Si CP-MAS-NMR. In addition, X-ray diffraction (XRD), inductively coupled plasma atomic emission spectroscopy (ICP-AES) and measurements of specific surface area by nitrogen adsorption (BET method) were carried out in order to obtain structural, textural and stability information about the solids. The samples were studied at different temperatures and heating time to optimize these parameters and to avoid a possible reduction of acidic properties by dehydroxylation. MAS-NMR and XRD results showed that the zeolite structure containing Nb did not undergo dealumination after thermal treatment, according to the presence of Si O Nb units on the zeolites structure in FTIR and Raman studies. Thermal analysis confirmed that Nb 2 O 5 impregnation reduced zeolite ZSM-5 dehydroxylation and thus promoted thermal stabilization. Nitrogen adsorption isotherms by the BET method indicated that surface area and pore volume decreased with the increase of Nb loading on the calcined samples at 450 °C. In addition, the nature of the zeolite active sites was investigated by spectroscopic and thermal analysis after pyridine adsorption. It was proposed that there are two different acidic sites (Bronsted and hydrogen bond site types) on the studied systems.

USY (ultrastabilized Y) and Ce/USY (5 wt.% supported) zeolite acidities were characterized by microcalorimetric and adsorption studies of pyridine using liquid phase (Cal-Ad), thermogravimetry, and infrared analysis. The average adsorption enthalpies determined by microcalorimetry were −125.0 kJ mol−1 for USY and −97.2 kJ mol−1 for Ce/USY. A heterogeneous distribution of acid sites with heats of adsorption ranging from −134.0 (maximum heat value for USY) to −73.5 (minimum heat value for Ce/USY) kJ mol−1 was found for both zeolites. A two-site model was best fitted by the Cal-Ad method for HUSY (n1 = 0.1385 mmol g−1 with ΔH1 = −134.0 kJ mol−1, and n2 = 0.7365 mmol g−1 with ΔH2 = −101.5 kJ mol−1) and Ce/HUSY (n1 = 0.0615 mmol g−1 with ΔH1 = −117.6 kJ mol−1, and n2 = 0.7908 mmol g−1 with ΔH2 = −83.6 kJ mol−1). DRIFTS measurements after pyridine adsorption showed that USY zeolite possesses only Bronsted acidity and that cerium impregnation leads to the appearance of Lewis sites. Based on these results, three families of acid strength were distinguished: (i) strong Bronsted sites (ΔH > −130 kJ mol−1); (ii) Bronsted sites with intermediate strength (−100

The interaction of hydrophobic chitin and chitosan with sodium dodecyl sulfate (SDS) has been studied by titration calorimetry at 298.15K. The nature of interaction of the surfactant and biopolymers was followed by enthalpy interaction profiles. The mixing enthalpy curves were determined by mixing SDS solutions above their critical micelle concentration with chitin and chitosan suspensions in different concentrations. The Gibbs free energy of aggregation values were -23.21, -22.71 and -21.53 kJ mol(-1) for chitin in 0.02, 0.05 and 0.1% concentration, respectively, and 28.30, 24.38 and 24.20 kJ mol(-1) for chitosan in 0.02, 0.05 and 0.1% concentration, respectively. The critical aggregation concentration (cac) obtained by calorimetric data gave 6.32, 7.07 and 9.14 mmol kg(-1) in 0.02, 0.05 and 0.1% concentration, respectively, for chitin and 2.09, 4.91 and 5.11 mmol kg(-1) for chitosan in 0.02, 0.05 and 0.1% concentration, respectively.

Zeolite beta acidity, activated at 550 degrees C, was characterized by calorimetric and adsorption studies of pyridine in cyclohexane (Cal-Ad). Two different acid sites were found: n(1) = 0.1612 mmol g(-1) with DeltaH(1) = -83.6 kJ mol(-1); and n(2) = 0.3820 mmol g(-1) with DeltaH(2) = -62.8 kJ mol(-1). Step calcinations followed by FTIR indicated n(1) as Lewis sites and n(2) as weak Brønsted sites. When activated at 450 degrees C, zeolite beta showed three different sites: n(1) = 0.0467 mmol g(-1) with DeltaH(1) = -227.3 kJ mol(-1); n(2) = 0.1163 mmol g(-1) with DeltaH(2) = -93.3 kJ mol(-1); and n(3) = 0.3322 mmol g(-1) with DeltaH(3) = -80.4 kJ mol(-1). Sites n(1) and n(2) were assigned as Brønsted centers, while n(3) as a combination of Brønsted and Lewis sites. These results suggest that the zeolite beta strongest Brønsted sites are converted to Lewis sites at 550 degrees C. These Lewis sites are not only related to extra-framework Al species, but also to aluminium atoms partially bonded to the zeolite framework, as evidenced by infrared bands at 3777 and 875 cm(-1). FTIR and thermogravimetric analyses of gas phase adsorbed pyridine were also used to investigate the materials acidity and a good agreement was found with Cal-Ad data. The results showed that the Cal-Ad method offers a more detailed description of the zeolite surface acidity by providing thermodynamic parameters not easily obtained by other techniques. A linear relationship between enthalpy and entropy values for several zeolites (ZSM-5, TS-1, MOR, Y and BEA) is also reported.

Acid strength distribution measurements of zeolite Y by a combined analysis of calorimetric and adsorption data, Cal-ad, for the reaction of zeolite Y with pyridine, 2,6-lutidine, 2,6-di-tert-butylpyridine, quinoline, tetrahydrothiophene and benzonitrile show the presence of three families of acid sites. The strongest sites (heats above −29 kcal mol−1) contain a significant number of Bronsted sites (n = 0.1 mmol g−1), which are located inside the large cages. The sites of intermediary strength (heats around −17 kcal mol−1) are of Lewis and Bronsted types and the weaker sites (heats below −10 kcal mol−1) contain significant hydrogen bonding. The strength of these sites is probably due to mutual interaction between Lewis and Bronsted sites. The accessibility on zeolite and the size of the probe molecules play fundamental role on the determination of acid site distribution. Application of the electrostatic–covalent model (ECW) to this acid provides quantitative parameters for determination of donor-acceptor contributions based on electrostatic (EA) and covalent (CA) intrinsic characters to each chemical bonding. The results demonstrate that zeolite Y has a stronger covalent character with EA = 5.25, CA = 6.89 (CA/EA = 1.31) consistent with softness properties suggested in the literature.