Zn_xMg_1‐xO Solid Solutions: Efficient Bifunctional Acid‐Base Catalyst for the synthesis of Methyl Ethyl Oxalate from Dimethyl Oxalate and Ethanol

Abstract

ZnO‐MgO composite catalysts were prepared by the coprecipitation method and used for the synthesis of methyl ethyl oxalate (EMO) from dimethyl oxalate (DMO) and ethanol (EtOH). The results of the SEM, XRD, FT‐IR and XPS confirmed that Zn2+ ions were incorporated into the cubic MgO lattice to form the solid solution structure over ZnO‐MgO composites catalysts with 6–18 mol% ZnO. The ZnO‐MgO composite catalysts with a solid solution structure have a large specific surface area, high medium acidic density, and medium basic density according to the results of N2 adsorption‐desorption, pyridine‐IR (Py‐IR) and NH3/CO2 temperature‐programmed desorption (NH3‐TPD/CO2‐TPD). The ZnxMg1‐xO solid solution with 18 mol% ZnO‐MgO (Zn0.18Mg0.82O) catalyst showed the highest catalytic activity with 71.98 % conversion of DMO and 67.36 % selectivity to EMO (DMO: EtOH molar ratio=1 : 2, reaction time=20 min, reaction temperature=80 °C and catalyst amount=1.5 wt%). The high catalytic activity was attributed to the solid solution structure with high medium acidic density and medium basic density. The conversion of DMO showed a positive linear correlation with the medium acidic density and medium basic density according to the correlation between catalytic activity and acidity‐basicity.

La‐Doped Mg‐Al Composite Oxides: Efficient Catalysts for the synthesis of Diethyl Carbonate via Transesterification of Ethylene Carbonate with Ethanol

“…The peak at 695 cm −1 is due to the stretching vibration of MgO, and the absorption peak corresponding to MgO of the HTC‐0.8La catalyst is red‐shifted (695 cm −1 shifted to 686 cm −1 ) compared to that of HTC‐0La (Figure S3). The wave number of FT‐IR is directly proportional to the bonding constants, which are inversely proportional to the ionic radii [31] . Since the ionic radius of La 3+ is larger than that of Mg 2+ , IR absorption peaks of MgO shifts to low wave numbers for the partial substitution of La 3+ for Mg 2+ , which is confirmed by the results of XRD.…”

“…The wave number of FT-IR is directly proportional to the bonding constants, which are inversely proportional to the ionic radii. [31] Since the ionic radius of La 3 + is larger than that of Mg 2 + , IR absorption peaks of MgO shifts to low wave numbers for the partial substitution of La 3 + for Mg 2 + , which is confirmed by the results of XRD. The band at 1056 cm À 1 is attributed to La 2 O 2 CO 3 .…”

“…The curve of HTC‐xLa exhibit three main desorption peaks, corresponding to the peak of weak base site (desorption temperature T<150 °C), the peak of medium base site (150 °C<T<350 °C) and the peak of strong base site (T>350 °C) respectively [9] . Weak base sites were correlated to OH groups on the catalyst surface, medium base sites were linked to metal‐oxygen pairs (Mg−O, Al−O, and La−O), and strong base sites were correlated with low‐coordination surfaces of the O 2− anion [24,31] . The desorption temperature of strong base sites of the samples gradually moved to a high temperature with the increase of La doping, which indicated that the introduction of La 3+ could increase the basic intensity of the catalysts [18] .…”

“…B TOTAL [b] HTC-0La to metal-oxygen pairs (MgÀ O, AlÀ O, and LaÀ O), and strong base sites were correlated with low-coordination surfaces of the O 2À anion. [24,31] The desorption temperature of strong base sites of the samples gradually moved to a high temperature with the increase of La doping, which indicated that the introduction of La 3 + could increase the basic intensity of the catalysts. [18] In terms of basic strength, the descending order of these catalysts was HTC-0La < HTC-0.4La < HTC-0.6La < HTC-0.8La < HTC-2.0La < HTC-1.0La.…”

Epsilon-Iron Carbide for the Hydrogenation of Carbonyl Groups in Esters

“…First, CO undergoes oxidative coupling to form DMO with >95% selectivity at 363–423 K and ambient pressure over Pd-based catalysts . Subsequently, a stepwise hydrogenation from DMO to methyl glycolate (MG), ethylene glycol (EG), and EtOH could be realized in a single-pass transformation, in which the selectivity of MG, EG, and EtOH is highly tunable by changing the catalysts and reaction conditions. − However, traditional Cu-based catalysts, albeit with high activity, inevitably lead to the formation of byproducts, such as ethers and C 3–4 alcohols, due to the dehydration and Guerbet reactions over acid–base sites in the catalysts . The replacement of methanol solvent by 1,4-dioxane could offer a higher selectivity from ∼80% to >90%, , yet limited in practical operation for the cycle of produced methanol.…”