SO₄^2–/ZrO₂ as a Solid Acid for the Esterification of Palmitic Acid with Methanol: Effects of the Calcination Time and Recycle Method

Abstract

Two types of SO4 2–/ZrO2 solid acid catalysts with various calcination times were prepared via incipient wetness impregnation of (NH4)2SO4 to hydrothermally synthesized ZrO2 and subsequently employed to catalyze the esterification of palmitic acid with methanol. The resulting catalysts were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and temperature-programmed oxidation (TPO) to elucidate their physicochemical properties, morphology, and deactivation mechanism. A calcination procedure is required to transform the amorphous ZrO2 into the crystal form. Both chelating and bridged bidentate SO4 2– coordinate with the ZrO2 surface. The calcination at 600 °C could well eliminate the water in the catalyst and a further higher temperature would accelerate the loss of SO4 2–. Long-time calcination also decreases the catalytic activity due to the transformation of monoclinic ZrO2 into tetragonal one and the slow leaching of SO4 2–. The catalytic activity increases with increasing catalyst loading amount, reaction temperature, and molar ratio of palmitic acid to methanol, while the heating temperature over 65 °C and excess methanol amount are unfavorable to the esterification reaction due to the low-boiling-point methanol and attenuation of the palmitic acid concentration. It appears that the reaction conditions of 65 °C, 6 wt % catalyst, 25:1 of methanol to palmitic acid, and 4 h reaction time are economically optimal under atmospheric pressure. The catalyst could not be well regenerated by the ultrasonic methanol washing method because of refractory organic residues. The catalyst activity could be well recovered without major activity loss by the calcination at 600 °C for 1 h. The catalyst deactivation is due to contamination by the refractory organic residues in the catalyst as well as by the leaching of SO4 2–, and thus both the calcination temperature and time should be strictly controlled to achieve a better catalyst lifetime.

Role of Sulfation of Zirconia Catalysts in Vapor Phase Ketonization of Acetic Acid

“…Sulfated zirconia (SZ) is well established as a robust and efficient solid acid catalyst for a variety of reactions of high industrial importance, such as hydrocarbon isomerization, methanol conversion to hydrocarbons, alkylation, acylation, esterification, dehydration, and Fischer–Tropsch processes. − More recently, sulfated zirconia has also emerged as a promising catalyst for several biorefinery processes, such as esterification, biodiesel preparation, − furfural synthesis − and conversion, − condensation of ketones, glycerol utilization, − and, conversion of CO 2 to light olefins . Among the biorefinery processes, the upgrading of biomass derived volatile fatty acids (C 3 –C 6 ) to corresponding ketones (ketonization reactions) is a promising strategy for the synthesis of biofuels.…”

Catalytic ozonation of dichloromethane at low temperature and even room temperature on Mn-loaded catalysts

“…Both M/Z-I and M/Z-II were monoclinic ZrO 2 (PDF# 37-1484). 40 The N 2 adsorption and desorption isotherms and pore size distribution curves of the ve Mn-loaded catalysts are displayed in Fig. S5.…”

Cation-doping strategies for tuning of zirconia acid–base properties

“…Zirconia (ZrO 2 ) is another example of a bifunctional catalyst which has found great interest in the materials science community as a prominent material for wide-ranging industrial applications, including biorefinery processes [ 8 , 17 – 22 ]. A plethora of modified ZrO 2 catalysts has been investigated; however, the use of dopants is probably still the most common approach for promoting changes in structure, stability, reactivity and selectivity of these systems.…”