A deactivation mechanism of sulfated titania in the esterification of acetic acid and n-butanol

Abstract

The present work systematically investigated the deactivation of sulfated titania in the esterification of acetic acid and n-butanol. Under the set conditions, sulfated titania was used 20 times and for 10 h accumulatively. The catalyst had the largest catalytic activity of 95.69 % at the second cycle and then the catalytic activities gradually dropped, and the last-cycle conversion of acetic acid was 46.15 %, suggesting a serious deactivation of the catalyst of sulfated titania after use in 20 cycles. XPS, FTIR, XRD, BET, TG-DSC, TEM and NH 3 -TPD were employed to characterize the new and deactivated catalysts, to systemically study the deactivation phenomena of sulfated titania and to find some reasons for the considerable deactivation of sulfated titania in the esterification. Some deactivation phenomena were observed on the deactivated catalyst when compared with the new one.(1) The deactivated catalyst decreased its acidity, based on the IR and NH 3 -TPD characteristic results. (2) The deactivated catalyst increased its surface specific area and its pore volume, and decreased its pore diameter, based on the BET characteristic results. (3) Some carbon deposits appeared on the surface of the deactivated catalyst, and some originally active sulfate groups may have been lost, poisoned and turned into less-catalytic and non-catalytic sulfur species based on the XPS and TG-DSC results. (4) The deactivated catalyst decreased its crystallinity based on the XRD results. (5) The deactivated catalyst diminished in particle aggregation, based on the SEM results. Thus, a deactivation mechanism is tentatively proposed. Namely, some originally active surface sulfate groups may have been gradually turned into the undesired free sulfuric acid and organic sulfate esters hydrolysis by H 2 O and their alcoholysis by n-butanol, which may lead to a gradual acidity degradation of the catalyst so as to lead to a gradual deactivation of sulfated titania. All the characteristic results more or less support the proposed deactivation mechanism.

Catalytic Activity of Sulfated and Phosphated Catalysts towards the Synthesis of Substituted Coumarin

“…Moreover, this class of catalysts can simply be retrieved and recycled, which classify these reactions as some of the green synthetic methodologies [2]. Amongst the abundant solid catalysts, sulfated metal oxides received more attention in recent years as potential catalysts for numerous reactions [3]. In comparison to acidic liquid catalysts, solid catalysts were found 2 of 18 to be less corrosive and environmentally friendly.…”

Synthesis of Ti(SO 4 )O solid acid nano-catalyst and its application for biodiesel production from used cooking oil

“…Several synthetic routes were applied for the preparation of heterogeneous catalysts including sol-gel [24][25][26][27], solvent-free [28,29] and hydrothermal methods [30][31][32][33]. Examples of heterogeneous catalysts include SO /TiO2 [30,[34][35][36][37],, SO /TiO2-SiO2 [38][39][40][41], SrO/SO -ZrO2 [29], SO /ZrO2 [17,[42][43][44], SO /TiO2-ZrO2 [45] and SO /SnO2 [17,46], which were considered for a good catalytic activity for the raw materials containing large amounts of FFA in biodiesel production. Among these, sulphated doped TiO2 is a good example of a solid super-acidic catalyst which is also used in the petrochemical industry and petroleum refining process [24,47] and showed better performances as compared to other sulphated metal oxides.…”

“…Some researchers have reported that the addition of sulphate ions to metal oxides enhances the acidic properties, catalytic activity, high selectivity, and causes less deactivation of the catalyst [25,[53][54][55][56]. However, Shi and Li [36] observed the deposition of carbon on the surface of sulphated metal oxide catalysts is the main reason to poison the catalytic activity of sulphated titania.…”