Hydrogenation of CO2 into Value-added Chemicals Using Solid-Supported Catalysts.

Reducing CO2 emissions is an urgent global priority. In this context, several mitigation strategies, including CO2 tax and stringent legislation, have been adopted to halt the deterioration of the natural environment. Also, carbon recycling procedures undoubtedly help reduce net emissions into the atmosphere, enhancing sustainability. Utilizing Earth's abundant CO2 to produce high-potential green chemicals and light fuels opens new avenues for the chemical industry. In this context, many attempts have been devoted to converting CO2 as a feedstock into various value-added chemicals, such as CH4, lower methanol, light olefins, gasoline, and higher hydrocarbons, for numerous applications involving various catalytic reactions. Although several CO2-conversion methods have been used, including electrochemical, photochemical, and biological approaches, the hydrogenation method allows the reaction to be tuned to produce the targeted compound without significantly altering infrastructure. This review discusses the numerous hydrogenation routes and their challenges, such as catalyst design, operation, and the combined art of structure-activity relationships for the various product formations.

ZSM-5 Catalysts for MTO: Effect and Optimization of the Tetrapropylammonium Hydroxide Concentration on Synthesis and Performance.

Light olefin production from methanol using various zeolite catalysts has industrial and economic importance considering the growth of the petrochemical market. Zeolites are generally synthesized using various organic templates as structure-directing agents (SDAs). In this study, synthesis of a series of ZSM-5 zeolites was performed systematically using the microwave-assisted crystallization method, and these samples were analyzed in detail to understand the effect of the SDA concentration. Powder diffraction, N2 adsorption, scanning electron microscopy, ammonia adsorption desorption, and 27Al and 29Si NMR spectroscopies were used for the characterization. The organic SDA tetrapropyl ammonium hydroxide (TPAOH/SiO2 mole ratio = 0.0500) is found to have an optimum concentration against the silica precursor for achieving the highest crystallinity, suitable morphology, ideal pore size, effective pore volume, and tuned microporous/mesoporous area. For samples with a template concentration ratio of 0.050 or higher, 29Si and 27Al NMR data revealed the presence of an intact ZSM-5 structure. Using a fixed bed reactor at 500 °C and atmospheric pressure, the catalytic performance of the selected catalysts from the series is investigated for the methanol-to-olefin conversion reaction. The sample with the highest crystallinity showed the best conversion, selectivity toward light olefins, and time on stream stability. It is also worth noting that the highest crystallinity, micropore area, and micropore volume are reached for the optimum value rather than the highest template concentration. This allows for a reduction in the template concentration and a move closer to a synthesis pathway benign to environment and economics.

Catalytic Cracking of n-Dodecane to Chemicals: Effect of Variable-Morphological ZSM-5 Zeolites Synthesized Using Various Silica Sources.

This study emphasizes tuning the synthesis conditions of MFI zeolites to achieve better catalytic properties by optimizing the mesoporosity, the balance between Brønsted and Lewis sites, and the zeolite particle sizes. The MFI zeolites were hydrothermally synthesized at various temperatures employing different silica sources. The synthesis temperature was varied between 110 to 180 °C at constant synthesis time (15 h). Different silicon sources led to variations in structure, morphology, and size of the MFI zeolite along with tuned Lewis and Brønsted acid sites in parallel correlation with shape selectivity of the reaction. The catalytic activities of synthesized zeolites were investigated in the catalytic cracking of n-dodecane to produce value-added chemicals. The zeolite synthesized at 180 °C using fumed silica presented the highest catalytic conversion (96.6%), while maximum light olefin gaseous products (73.1%) were obtained for the sample synthesized at 140 °C using tetraethyl orthosilicate as the silica source. The MFI zeolite synthesized at 180 °C employing tetraethyl orthosilicate as a silica source facilitated the formation of both naphthenes and aromatics (71.3%) as major liquid products.

Nano BEA zeolite catalysts for the selective catalytic cracking of n-dodecane to light olefins.

Nano BEA zeolite catalysts were synthesized and modified by desilication and then ion-exchanged with Co. The desilication was carried out using 0.1 M of NaOH. The synthesized and modified nano BEA catalysts were characterized via different characterization techniques. Ammonia temperature program desorption (NH3-TPD) and the pyridine Fourier transform infrared (pyridine-FTIR) were utilized to investigate the acidity of catalysts. X-ray diffraction (XRD), 27Al and 29Si nuclear magnetic resonance (NMR) spectroscopy techniques were used to examine the structure of the catalysts. The XRD patterns of the as-synthesized nano BEA catalysts were identical to that of the reference, while the NMR analysis revealed the distribution of silicon and aluminum in the BEA structure. The scanning electron microscope (SEM) analysis confirmed that the fabricated catalysts were less than 100 nm. The desilication and Co ion-exchange altered the acidity of the catalyst. The catalysts were evaluated in the cracking of sssssss to light olefins in the temperature range from 400 °C to 600 °C. The conversion increased with the increase in the reaction temperature for both catalysts; the conversion was above 90% for the Co-BEA catalyst at a temperature above 450 °C. The yield of light olefins also increased at higher temperatures for both catalysts, while at a lower temperature the yield to light olefins was ca. 40% over that of Co-BEA.