Current Catalysis - Volume 9, Issue 1, 2020

Background: The Fischer-Tropsch Synthesis (FTS) remains an important process for motor fuel production from CO and H2. The composition of the FTS products (hydrocarbon mixtures) depends on the properties of a catalyst and on the process conditions. Summary: The introduction of zeolites into catalytic systems can alter the molecular weight distribution paving the way to tailor-made fuels, as was revealed by recent research results produced in the laboratories worldwide. The AlO4 and SiO4 tetrahedrons, which constitute the zeolites, are able to transfer electrons and ions in a way, which makes water-zeolite interfaces capable of initiating active carbonium ions. It was shown in a number of works that the water-zeolite interface plays a key role in diverting the FTS from the classical route. Conclusion: This review gives a critical analysis of literature data on the role of water-zeolite interfaces on FTS cobalt catalysts and on the interactions of hydrophobic and hydrophilic zeolites with water.

Reduction of carbon dioxide into formic acid using transition metal complexes as catalysts is a research area of abiding importance. Although ruthenium(II) complexes as ‘molecular catalysts’ have received much attention, use of ruthenium(III) complexes in the selective reduction of carbon dioxide into formic acid has recently been explored. This review focuses on the recent research progress in the use of a ruthenium(III) complex containing the ‘edta’ ligand (edta4- = ethylenediaminetetraacetate) as catalyst or mediator in the catalytic, electro-catalytic and photocatalytic conversion of bicarbonate to formate selectively. Details of the reaction mechanism pertaining to the overall catalytic process are discussed.

Background: In this review, different heterogeneous catalysts based on acid, base, metal and enzymes are discussed for the synthesis of industrially relevant perfumes and flavor compounds. These molecules are mainly produced by a variety of reaction pathways such as esterification, isomerization, hydration, alkylation, hydrogenation, oxidation, etc. All these reactions are discussed thoroughly for the synthesis of vital aromatic compounds. The review also summarizes various recent technologies applied for designing new catalysts to obtain the maximum yield of the desired product. Overall, this review highlights the green, clean and eco-friendly processes which can be industrially accepted for the synthesis of perfumes, flavors and fragrances. Objective: The objective of the current review was to emphasize on the synthesis of industrially important perfumes and flavor molecules such as α-terpineol, cyclohexyl esters, thymol, raspberry ketone, etc. using heterogeneous catalysts. Results: Three hundred and eight papers are reported in this review, the majority of which are on heterogeneous catalysis for the synthesis of molecules which impart flavor or possess perfumery characteristics. Among all, the preparation of esters is highlighted as they represent an imperative functional group in aroma chemicals. Conclusion: The review confirms the need for heterogeneous catalysis in pollution-free and costeffective synthesis of flavor and perfumery compounds.

Hydrogenation of CO2 to energy-rich products over heterogeneous metal catalysts has gained much attention due to their commercial applications. Specifically, the first-row transition metal catalysts are very rarely reported and discussed for the production of formic acid from the hydrogenation of CO2. Herein, hydrotalcite supported copper metal has shown activity and efficiency to produce formic acid from the hydrogenation of CO2, without adding any additional base or promoter and was effectively recycled 4 times after separating by simple filtration without compromising the formic acid yield. Hydrotalcite supported copper-based catalyst (Cu-HT) was synthesized through the coprecipitation method and used as a heterogeneous catalyst for the hydrogenation of CO2. The precise copper metal content determined by ICP in Cu-HT is 0.00944 mmol. The catalyst afforded maximum TOF, 124 h-1 under the employed reaction conditions: 100 mg catalyst, 60 °C, 60 bar total pressure of CO2/H2 (1:1, p/p) with 60 mL of mixed methanol:water (5:1, v/v) solvent. Cu-HT catalyst was synthesised and thoroughly characterized by FT-IR, PXRD, SEM, TEM, XPS and BET surface area. The first-order kinetic dependence with respect to the catalyst amount, partial pressures of CO2, and of H2 was observed and a plausible reaction mechanism is suggested. Background: CO2 hydrogenation to energy-rich products over heterogeneous metal catalysts has gained much attention due to their commercial applications. Specifically, the first-row transition metal catalysts are very rarely reported and discussed for the production of formic acid from the hydrogenation of CO2. Objective: The aim is to investigate the heterogeneous catalyst systems, using solid soft base hydrotalcite supported Cu metal-based catalyst for effective and selective hydrogenation of CO2 to formic acid. Methods: The Cu –HT catalyst was synthesized and characterized by FT-IR, PXRD, SEM, TEM, XPS and BET surface area in which the precise copper content was 0.00944 mmol. The Cu-HT catalysed hydrogenation of CO2 was carried out in the autoclave. Results: The Cu-HT catalyst afforded maximum TOF of 124 h-1 under the employed reaction conditions: 100 mg catalyst, 60 °C, 60 bar total pressure of CO2/H2 (1:1, p/p) with 60 mL of mixed methanol: water (5:1, v/v) solvent, without adding any additional base or promoter and was recycled 4 times by simple filtration without compromising the formic acid yield. Formation of formic acid was observed to depend on the amount of the catalyst, partial pressures of CO2 and H2, total pressure, temperature and time. Conclusion: Cu-HT based heterogeneous catalyst was found to be efficient for selective hydrogenation of CO2 to formic acid and was effectively recycled four times after elegantly separating by simple filtration.

Background: Metal oxide or metal oxide composite nanoparticles are attaining tremendous importance due to their catalytic activities for various organic transformations. Objective: To report the one-pot synthesis of xanthene derivatives prepared by ZnS-Fe2O3-Ag composite under solvent-free conditions. Method: To prepare nanocomposite by a facile and simple hydrothermal approach. Results: The prepared composite is smaller (17.56 nm) in size and can be easily separable, recycled and reused six times without any significant loss of catalytic activity with excellent yields. In short reaction time, great catalytic activity was perceived with no co-catalyst and any other activator. Conclusion: In conclusion, ZnS-Fe2O3-Ag composite provides a simple, economical, efficient and greener method for the synthesis of one-pot multicomponent reaction of aldehyde with 1,3-diketones under solvent free conditions for the synthesis of 1,8-dioxooctahydro xanthenes. In short reaction time, great catalytic activity was perceived with no co-catalyst and any other activator.

Background: Hydrogen has been considered the energy source of the future and one of the processes for its production is the methane steam reforming. The catalyst used industrially is Ni/Al2O3 and the addition of promoter oxides can be an alternative to improve the performance of this catalyst, which suffers from coke formation and sintering. Objective: Evaluate the role of niobia on catalytic activity and stability. Methods: Ni/x%Nb2O5/Al2O3 (x = 5, 10 and 20) catalysts were synthesized via coprecipitation-wet impregnation method and characterized by X-ray fluorescence (XRF), N2 adsorption-desorption, X-ray diffraction (XRD), temperature- programmed reduction (TPR), temperature-programmed desorption of ammonia (TPD-NH3), etc. Finally, the catalysts were tested for methane steam reforming reaction. Results: All niobia-doped catalysts presented similar values of methane conversion and when comparing with Ni-Al, the addition of niobia slightly improved the methane conversion. In the stability test at 800°C, all doped and non-doped catalysts did not deactivate during the 24 h of reaction. Conclusion: The addition of 10 and 20 wt.% of niobia had a significant promoter effect over Ni/Al2O3 catalyst in terms of activity and stability at 800 °C and the sample with 20 wt.% of niobia presented lower coke formation.