Carbon Dioxide Fixation into Chemicals (Methyl Formate) at High Yields by Surface Coupling over a Pd/Cu/ZnO Nanocatalyst

Abstract

In recent years, the carbon dioxide (CO 2 ) issue has become the focus of attention because of the position of CO 2 as the primary greenhouse gas and the implication of its emissions on the problem of climate change. Burning fossil fuels releases the CO 2 stored millions of years ago. Deforestation releases the carbon stored in trees, resulting in more CO 2 in the atmosphere. The resulting climate change is an immediate threat to our security and prosperity, as the global food supplies will be compromised. Therefore, in pursuit of a stable climate, there is an urgent need to construct a low carbon global economy. For example, the U.K. government targets a 60% cut in emissions by 2050 1 as a necessary step for the development of a sustainable economy. Thus, an instantaneous response for research studies in the chemistry of CO 2 including its activation, utilization, and fixation is urgently needed. Apart from the physical storage of CO 2 into depleted oil/gas/coal reservoirs, chemical fixation of CO 2 has attracted additional attention as a possible way to manufacture useful chemicals in some specific locations. As a result, the activation of CO 2 at high yields appears to be the essential step to achieve the above objective. However, there has been limited work in literature reporting a catalytic approach to activate and to fix CO 2 under industrial applicable conditions, despite the fact that this process has been recognized as a significant innovation to chemical industry. 2 Most previous attempts were unable to attract industrial attention as they suffer from either the use of expensive but non-robust homogeneous catalysts or the use of peculiar reaction conditions (requires excess ligand(s) and solvents at extreme conditions). 3 Here, we demonstrate a one-step catalytic fixation of CO 2 to methyl formate (MF) in liquid phase under mild industrial applicable conditions by using a new concept of coupling surface formate species formed from CO 2 on solid catalyst with excess methanol in hydrogen to form the MF, and the quantity of the product is found to greatly exceed the surface coverage of the catalyst by >45-fold. As a result, we report, for the first time, that the optimum Pd/Cu/ZnO/alumina nanocatalyst prepared from simple co-precipitation is capable of activating gaseous CO 2 to condensable MF at high yields (>20%) with excellent selectivity (>96%).As an initial effort, co-precipitated Cu/ZnO/alumina (Cat) was used as the catalyst for the proof of concept of surface coupling with blended molecule, which is an industrial catalyst for water gas shift reaction, WGS (and also reversed reaction, RWGS), where formate species is believed to be the intermediate species. 4 The use of hydrogen to activate CO 2 to useful chemicals at low temperature could be commercially viable with regard to future hydrogen availability from hydrocarbon reformations with carbon capture/storage and from catalytic water splitting via solar energy. Thus, screening of different solvent molecules in order to identify a candidate that...

Methanol Synthesis from Industrial CO2 Sources: A Contribution to Chemical Energy Conversion

“…Methanol can react with the formate species adsorbed on the catalyst's surface, which are intermediates during methanol synthesis and reverse water gas shift reaction, to produce methyl formate by the reaction given in Eq. 3 [28].…”

“…Methanol decomposition was studied [28] by injections of methanol at 473 and 573 K over the Cu/ZnO/Al 2 O 3 catalyst. According to the obtained results the methyl formate amount decreases and the CO amount increases with time.…”

A Study of Methyl Formate Production from Carbon Dioxide Hydrogenation in Methanol over a Copper Zinc Oxide Catalyst

“…As a result, the data obtained from gas phase GC-FID analysis can be combined with the data obtained from liquid phase 1 H-NMR analysis to provide a comprehensive chemical analysis within the calibrated range. In our previous communication [5], we reported a satisfactory carbon mass balance for this reaction. For the triethylamine promotion study, a nitrogen mass balance of over 95% was obtained (from NMR).…”

“…It was found from the previous feasibility study [5] that methanol can couple with formate species adsorbed on the catalyst to produce MF. Esterification of formate species with methanol possibly catalyzed by acid sites on the catalyst was a probable pathway on the copper zinc oxide surface under the reaction conditions applied.…”

“…Subsequently, we have clearly demonstrated the catalytic hydrogenation of CO 2 to MF in the presence of liquid methanol by employing a Pd/Cu/ZnO/Al 2 O 3 nanocatalyst system [5]. The quantity of the MF produced was found to greatly exceed the maximum amount of surface species covering the catalyst by many folds ([45 times).…”