10-ring Zeolites: Synthesis, characterization and catalytic applications

Current Challenges and Perspectives for the Catalytic Pyrolysis of Lignocellulosic Biomass to High-Value Products

Lignocellulosic biomass is an excellent alternative of fossil source because it is low-cost, plentiful and environmentally friendly, and it can be transformed into biogas, bio-oil and biochar through pyrolysis; thereby, the three types of pyrolytic products can be upgraded or improved to satisfy the standard of biofuel, chemicals and energy materials for industries. The bio-oil derived from direct pyrolysis shows some disadvantages: high contents of oxygenates, water and acids, easy-aging and so forth, which restrict the large-scale application and commercialization of bio-oil. Catalytic pyrolysis favors the refinement of bio-oil through deoxygenation, cracking, decarboxylation, decarbonylation reactions and so on, which could occur on the specified reaction sites. Therefore, the catalytic pyrolysis of lignocellulosic biomass is a promising approach for the production of high quality and renewable biofuels. This review gives information about the factors which might determine the catalytic pyrolysis output, including the properties of biomass, operational parameters of catalytic pyrolysis and different types of pyrolysis equipment. Catalysts used in recent research studies aiming to explore the catalytic pyrolysis conversion of biomass to high quality bio-oil or chemicals are discussed, and the current challenges and future perspectives for biomass catalytic pyrolysis are highlighted for further comprehension.

Computational elucidation of the aging time effect on zeolite synthesis selectivity in the presence of water and diquaternary ammonium iodide

An example of zeolite selectivity (MFI → MOR) driven by synthesis aging time has been studied. Using N,N,N',N'-tetramethyl-N,N'-dipropyl-ethylenediammonium diiodide (TMDP) as an organic structure-directing agent (OSDA), the zeolite phases obtained at 2 h (MFI 97%), 8 h (MFI 84%, MOR 16%) and 24 h (MFI 43%, MOR 57%) have been characterized by powder X-ray diffraction. The results suggest that at intermediate aging time, namely 8 h and 24 h, the dominant phase (MFI) is displaced by MOR. Different techniques (FT-IR, Raman, ¹³C MAS NMR, TGA/DTG and HC microanalysis) have been employed to verify the OSDA integrity and occlusion inside the zeolite micropores as well as to quantify the water and OSDA loading. The ¹H MAS NMR of the as-made occluded zeolite was compared with the spectra of TMDP and the recovered OSDA from the sample by extraction with water. The comparison indicated that TMDP was not structurally intact, indicating the chemical transformation of TMDP to imidazolinium homologues through the Hofmann degradation process. Furthermore, careful acidic breakdown of the aluminosilicate shell, covered on the zeolite samples by hydrofluoric acid, revealed that the remaining OSDA had been partially degraded to lower molecular weight ammonium salt, confirmed by ¹H NMR and mass spectrometry measurements. A computational study was performed by using a force field based methodology, including accurate loading of water and OSDA in the zeolite (MFI and MOR) unit cells. The results show an important contribution of the presence of water. The samples with larger aging time (8 h and 24 h) incorporate less water and show partial TMDP degradation, whilst at the shortest aging time (2 h), there is a larger water content and TMDP remains intact. The larger accessible volume of MFI justifies that this is the dominant phase at short aging times (large water content) since it can accommodate a larger number of water molecules than MOR. The OSDA partial degradation also plays a role. At longer aging times the partial OSDA decomposition has been considered in the models by including TMDP + Imidaz, which is more stabilized by MOR, whilst at shorter aging times the only OSDA present, TMDP, is better stabilized by MFI.