Synthesis of Al-Modified SBA-15-Supported Ru Catalysts by Chemical Fluid Deposition for Hydrogenation of Dimethyl Terephthalate in Water

Abstract

Uniformly dispersed 5 wt % ruthenium catalysts supported on Al x SBA-15 (x = Si/Al ratio) were prepared by chemical fluid deposition employing supercritical CO2 as the solvent for hydrogenating dimethyl terephthalate to dimethyl 1,4-cyclohexanedicarboxylate in water. Complete conversion of dimethyl terephthalate was achieved over a Ru5/Al20SBA-15 catalyst having the highest number of Lewis acid sites at 100 °C and 4.14 MPa H2 pressure in 1 h. Here, 100% selectivity with a dimethyl 1,4-cyclohexanedicarboxylate yield of 93.4% was observed in 0.5 h due to complete cutoff of hydrocracking byproducts at shorter reaction times. Al modification enhanced selectivity of the catalysts toward dimethyl 1,4-cyclohexanedicarboxylate by governing the distribution of Lewis and Brönsted acid sites in the support. Water as a functional solvent enriched the hydrogenation of dimethyl terephthalate via an on-water mechanism. The Ru5/Al20SBA-15 catalyst was stable over five cycles. Greener catalyst synthesis, use of water, mild reaction conditions, and high atom economy led the proposed system to be a greener sustainable process.

On-Water Hydrogenation of Polyethylene Terephthalate to Environmentally Friendly Polyester by the Catalyst Rh2.5Pt2.5/SBA-15

“…Following the first impregnation step, the complete removal of THF was ensured using a rotary evaporator. The dried catalyst powders were then transferred to an autoclave and scCO 2 treatment was carried out at a pressure of 2500 psi and a temperature of 40 °C for 2 h. A CO 2 pressure higher than its critical pressure was used to enhance its solubilizing capability toward organometallic precursors Rh­(acac) 3 and Pt­(acac) 3 based on previous knowledge for the synthesis of SBA-15-supported Rh–Pt bimetallic catalysts using CFD . For post-scCO 2 treatment, the autoclave was depressurized slowly, and the collected powders were subjected to chemical reduction using H 2 (20 mL/min) at 400 °C for 4 h. The reduced catalyst powders were marked Rh x Pt y /SBA-15, where x and y represent the theoretical metal loadings of Rh and Pt, respectively.…”

“…It has been previously reported that when using water as a solvent for the hydrogenation of aromatic ring compounds the reaction rates were amplified considerably even though the reactants were insoluble in water. − The formation of a H 2 bond at the aqueous catalyst–reactant interface, known as the on-water mechanism, was identified as the major reason for this amplification. Through the on-water mechanism, polarization of the aromatic rings of the reactant takes place thereby increasing the susceptibility of the aromatic rings to be attacked by spillover H atoms and undergo hydrogenation by the active metals of catalysts employed.…”

“…Previously, silica-supported Rh and Rh–Pt catalysts synthesized using CFD were tested by our group to be superior to catalysts synthesized by conventional techniques such as wet impregnation for the hydrogenation of aromatic compounds. , SBA-15 was chosen as the support material for this study owing to not only its good hydrothermal stability and well-ordered structure but also its hydrophilic nature that ensured a good dispersion of the catalyst in water. Moreover, the presence of Si–OH groups on its surface was also expected to assist in the advent of a higher degree of on-water mechanism when water was used as the solvent through H-bonding at the catalyst–reactant interface . Rh–Pt synergy for the hydrogenation of not only PET but also other compounds containing aromatic rings such as DMT and bisphenol A-type epoxy resin, where Rh played the primary role of selectively hydrogenating the aromatic rings while Pt assisted in the orientation of the aromatic rings to the active sites of the catalyst in a bridge manner on Pt(111) for easier hydrogenation, has been well documented. ,,− Moreover, as reported by Greely and Mavrikakis, the binding energy (BE) for H 2 on the surface of Rh–Pt alloy NPs (2.57 eV) is lower than that on individual Rh (2.81 eV) or Pt (2.78 eV), leading to easier dissociation and spillover of H atoms on the Rh–Pt surface.…”

Recent developments in metal-doped SBA-15 catalysts for heterogeneous catalysis and sustainable chemistry

“…Various synthesis procedures have been employed, which include direct synthesis, postsynthetic wet impregnation, Sonication, post-grafting, Insitu-method, the chemical fluid method, evaporation induced wet impregnation, as well as immobilization [38][39][40][41][42][43][44][45] . Table-1 illustrates the different types of synthesis of functionalized metal-doped SBA-15 and their textural properties.…”

“…Biomass-derived furfural such as furfuryl alcohol, methyl levulinate, Maleic anhydride, succinic acid, and many more chemicals intermediate is prepared by renewable resources. These chemicals find extensively used for the synthesis of the valuable compound for flavoring agents, fuel additives, and fine chemicals [36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53] . In recent times, However, the author invented continuous production of GVL, and reported the 77% yield of GVL in the 24h stream by using Co-SBA-15 catalyst under atmospheric H 2 pressure [36][37][38] .…”