Thermo–Photo Catalysis for Methanol Synthesis from Syngas

Abstract

It is well-known that the synthesis of methanol from syngas is based on thermal catalysis (TC). However, in this work, light was introduced into the thermal catalytic process, creating a novel thermo–photo catalysis (TPC) for methanol production from syngas over a Cu/Zn/Al catalyst. It was demonstrated that the yield of methanol from the TPC process was 2.8 times that from the TC process at a catalyst temperature of 350 °C. Unlike the general recognition that the catalytic performance is mainly dependent on the temperature of the catalyst surface, TPC is also greatly influenced by the reactant temperature. The yield of methanol was enhanced 3.3 times by increasing the reactant temperature from 93 to 260 °C at a constant catalyst-surface temperature of 350 °C. Furthermore, although Cu+ is the active site for thermal catalysis, Cu++ plays an important role in thermo–photo catalysis. This work provides insights into the synergistic effect of thermal energy and photoenergy in thermo–photo catalytic syngas conversion.

Distinct Pathways in Visible-Light Driven Thermo-Photo Catalytic Methane Conversion

“…The combination of thermal catalysis and photocatalysis, which leads to a novel thermo-photo catalytic process, has hardly been investigated for CH 4 conversion. As demonstrated in our previous work, thermal energy could make the reactants more active, thus providing a sufficient driving force for visible-light photocatalysis. − Photoenergy in turn could significantly lower the energy input in traditional thermal catalysis. ,, The synergetic effect of thermal and photo energies offers the possibility for realizing both high efficiency and low cost. Nevertheless, the participation of both thermo- and photoenergies makes this process more complex, and different products might be resulted via different pathways.…”

Thermo-photo catalysis: a whole greater than the sum of its parts

“…Furthermore, the power required to shine the light is lower than that required to heat the reactor, so the overall energy consumption can be reduced by introducing photo energy and lowering thermal input for thermal catalytic systems. 34,73,74 Secondly, the introduction of photo energy can tune the catalytic selectivity toward some products which cannot be attained in traditional thermal catalysis. 36,56,75,76 Most representatively, while thermal catalytic alkyne hydroamination at 30-100 1C over Au-Co/ZrO 2 catalyst led to very low selectivities toward imine (below 10%), thermo-photo catalysis in the same temperature range showed high selectivities surpassing 90% owing to photo-induced intramolecular electronic transitions.…”

“…In contrast to the local heating in photothermal reactors which is only for the catalyst, the external heating devices typically provide the global heating for both catalyst and reactants, thus enhancing the catalytic activity. 34 While, a few devices provide single-plane heating, which may result in the temperature gradient for thick catalyst beds. 44,175 The typical externally heated batch reactor and flow reactor are illustrated in Fig.…”

“…21 Since then, a rapid and exciting development in thermo-photo catalysis has been witnessed with an emphasis on catalyst design and catalytic performance enhancement. So far, thermo-photo catalysis, as a whole greater than the sum of its parts (individual thermal catalysis and photocatalysis), has been applied in a wide range of chemical processes such as CO 2 reduction, [22][23][24][25][26] CH 4 oxidation, [27][28][29][30][31][32][33] CO conversion, [34][35][36][37][38] production, 21,[39][40][41][42] N 2 fixation, [43][44][45][46] pollutant degradation, [47][48][49][50][51] and organic synthesis, [52][53][54][55][56] showing high activity, tuneable selectivity, and excellent stability under mild conditions at low cost, owing to the synergetic effects of thermal and photo energies (Fig. 2).…”

Highly efficient visible-light photocatalytic ethane oxidation into ethyl hydroperoxide as a radical reservoir

“…This is because the kinetic energy of the reactants increased by the temperature rise can compensate the potential driving force for corresponding redox reactions. As a result, the visible-light driven photocatalytic activities were significantly improved in a series of chemical processes including water splitting, 37–39 CO 2 reforming of CH 4 , 40 steam reforming of CH 4 , 41 CO hydrogenation, 42 and CO 2 hydrogenation. 43 Based on our previous successes, introducing thermal energy is expected to enhance the efficiency of ethane oxidation under visible light irradiation, which constitutes the second hypothesis of this work.…”