Direct Oxidative Esterification of Propionaldehyde to Methyl Propionate Using Heavy-metal-free Palladium Catalysts under Pressurized Oxygen

Abstract

The use of pressurized oxygen greatly enhanced catalytic activity for oxidative esterification of propionaldehyde to methyl propionate with methanol using heavy-metal-free Pd/C and Pd/Al2O3. For example, the conversion of propionaldehyde, the selectivity to methyl propionate, and the yield of the propionate using 5 % Pd/Al2O3 were 99.9, 62.7, and 62.6 %, respectively, at 1.5 MPa of oxygen gas and 333 K. This result demonstrated that Pb doping of Pd catalysts was not needed to achieve comparable activity, which runs contrary to previous reports, in which it had been suggested that loading of Pd catalysts using a heavy metal such as Pb was needed for the great activity such as 93.2, 76.8, and 71.6 % of the conversion of propionaldehyde, the selectivity to methyl propionate, and the yield of the propionate, respectively, at 0.3 MPa of oxygen gas and 353 K using 5 % Pd/Al2O3 doped with 5 % Pb.

The Oxidative Esterification of Propionaldehyde to Methyl Propionate in the Liquid-Phase Using a Heterogeneous Palladium Catalyst

“…Symbols: ○, the conversion of PA; □, the selectivity to MP; △ , the yield of MP; and closed bar, the MP As shown in Figure 2, the conversion of PA increased with the reaction time while the selectivity to MP was essentially constant regardless of the reaction time, which resulted in an increase in the yield of MP. During the conversion of PA, the selectivity to MP, and the yield of MP after 6 h were 99.9, 61.9 and 61.8%, respectively, which was essentially identical to the activity reported under the same conditions (99.9, 62.7 and 62.6%, respectively) in our previous paper (Sugiyama et al, 2011). This data was evidently lower than that (93.2, 76.8 and 71.6%, respectively) reported by Diao et al (2009) at 0.3 MPa of O 2 and 353 K after 2 h, although the reaction temperature in the present reaction was 20 K lower than that reported by Diao et al (2009), and the weight of the catalyst (1.0 g) was four-fold greater than that reported by Diao et al (2009).…”

“…As pointed out in Section 2.1., the surface area and dispersion of the Pd metal contributed to the catalytic activity. However, as shown in our previous paper (Sugiyama et al, 2011), the activity of Pd/C, with a greater surface area (946 m 2 /g) and a greater dispersion of Pd (13.9%), was evidently lower than that using Pd/Al 2 O 3 . This indicated that the nature of the influence of Pd over the supports, C and Al 2 O 3 , might have differed.…”

“…A third example was the direct oxidative esterification of propionaldehyde to methyl propionate using Pd/Al 2 O 3 in a methanol solution. For the present study, Diao et al (2009) had reported that Pd/Al 2 O 3 doped with Pb showed activity as great as 93.2% for the conversion of propionaldehyde, 76.8% of the selectivity for methyl propionate, and a 71.6% yield of methyl propionate at 0.3 MPa of O 2 and 353 K. However, our most recent study using heavy-metal-free Pd/Al 2 O 3 showed comparable activity that included a 99.9% conversion of propionaldehyde, 62.7% selectivity to methyl propionate, and a 62.6% yield of methyl propionate obtained at 1.5 MPa of O 2 and 333 K, indicating potential for the use of a heavy-metal-free Pd catalyst in various catalytic reactions (Sugiyama et al, 2011).…”

“…In our previous paper (Sugiyama et al, 2011), catalysis using Pd/C under atmospheric pressure showed that the doping of Pd/C with heavy metal (tellurium) was unnecessary, while that using Pd/Al 2 O 3 (62.6% of the yield of MP at 1.5 MPa of O 2 and 333 K after 6 h), which was evidently greater than when Pd/C (38.5% of the yield of MP under the same reaction conditions) was used, was briefly described. Therefore, the time-course of the esterification using 1.0 g of Pd/Al 2 O 3 and 75.0 mmol of PA at 1.5 MPa of O 2 and 333 K was again examined.…”

“…Any leaching of Pd from the catalyst during the preparation was not detected. Catalytic activity was tested in a magnetically-stirred stainless steel autoclave (85 mL) reactor (Sugiyama et al, 2011) using the following procedures according to the results from a previous study (Diao et al, 2009). A given amount of the catalyst (1.0 or 0.5 g) was added to the reactor along with a 25 mL methanol solution containing 75 or 37.5 mmol of propionaldehyde.…”