Diffusion of methyl oleate in hierarchical micro-/mesoporous TS-1-based catalysts probed by PFG NMR spectroscopy

Partial Hydrogenation of Palm Oil-Derived Biodiesel over Ni/Electrospun Silica Fiber Catalysts

Given the high accessibility of reactants to the active metal sites of fibrous catalysts, in this research, an electrospun silica fiber was applied as a support of nickel catalysts (Ni/SF) for the partial hydrogenation of palm oil fatty acid methyl ester (FAME) in a fixed-bed reactor. The textural properties, reducibility, Ni dispersion and morphology of Ni/SF catalysts were characterized and compared to those of a Ni/porous silica ball (Ni/SB). Under 1 bar H2 pressure at 140 °C, the 30 wt% Ni/SF catalyst exhibited a high turnover frequency (TOF) of 1396 h−1 to convert methyl linoleate (C18:2) to more saturated structures. On the other hand, the system using Ni/SB catalysts showed a TOF of only 141 h−1. This result was due to the effect of the higher acidity of the silica fiber, which promoted the higher adsorption of polyunsaturated portions in FAME. The non-porous characteristics and open morphology of the Ni/SF catalysts also allowed FAME and H2 molecules to easily access the Ni active sites deposited on the surface of the silica fiber and suppressed the selectivity to cis–trans isomerization. Stability testing of the Ni/SF catalyst showed that the C18:2 conversion decreased from 71% to 60% after long-term operation for 16 h possibly due to the weak metal–support interaction that facilitated Ni particle loss from the catalyst surface.

Synthesis of highly active ETS-10-based titanosilicate for heterogeneously catalyzed transesterification of triglycerides

In this contribution, the preparation of hierarchically structured ETS-10-based catalysts exhibiting notably higher activity in the conversion of triolein with methanol compared to microporous titanosilicate is presented. Triolein, together with its unsaturated analog trilinolein, represent the most prevalent triglycerides in oils. The introduction of mesopores by post-synthetic treatment with hydrogen peroxide and a subsequent calcination step results in the generation of an additional active surface with Brønsted basic sites becoming accessible for triolein and enhancing the rate of transesterification. The resulting catalyst exhibits a comparable triolein conversion (≈73%) after 4 h of reaction to CaO (≈76%), which is reportedly known to be highly active in the transesterification of triglycerides. In addition, while CaO showed a maximum conversion of 83% after 24 h, the ETS-10-based catalyst reached 100% after 8 h, revealing its higher stability compared to CaO. The following characteristics of the catalysts were experimentally addressed - crystal structure (X-ray diffraction, transmission electron microscopy), crystal shape and size (scanning electron microscopy, laser diffraction), textural properties (N2 sorption, Hg porosimetry), presence of hydroxyl groups and active sites (temperature-programmed desorption of NH3 and CO2, 29Si magic angle spinning nuclear magnetic resonance (NMR)), mesopore accessibility and diffusion coefficient of adsorbed triolein (pulsed field gradient NMR), pore interconnectivity (variable temperature and exchange spectroscopy experiments using hyperpolarized 129Xe NMR) and oxidation state of Ti atoms (electron paramagnetic resonance). The obtained results enabled the detailed understanding of the impact of the post-synthetic treatment applied to the ETS-10 titanosilicate with respect to the catalytic activity in the heterogeneously catalyzed transesterification of triglycerides.