Methanol-to-olefins catalysis on window-cage type zeolites/zeotypes with syngas co-feeds: Understanding syngas-to-olefins chemistry

Evaluating the Role of Descriptor- and Spectator-Type Reaction Intermediates During the Early Phases of Zeolite Catalysis

“…Increasing the partial pressure of hydrogen led to increased hydrogen transfer activity over ZSM-5. These control experiments were also consistent and complementary to a series of recent publications from the Bhan group. ,, Therein, Arora et el. reported that the coprocessing of H 2 with methanol under pressure over numerous zeolites (CHA, AEI, FER, BEA) led to an enhancement of the catalyst lifetime compared to He cofeeds under identical reaction conditions. , They correlated the diminishing catalyst deactivations with the scavenging of HCHO-mediated alkylation routes over zeolite, as discussed in Section .…”

“…It is important to remember that this control experiment was been performed only over the standalone zeolites, without involving any metallic catalyst. This observation justifies the mechanistic significance of a ketene-based reactive intermediate over the zeolite and the impact of the Koch-carbonylation mechanism. ,, Similarly, Dokania et al also reported an analogous observation while performing cofeeding experiments with 13 CO and ( 12 C) ethylene over a Ca-impregnated zeolite to mimic the CO 2 hydrogenation (reaction conditions: 350 °C, 3 MPa, CO 2 /H 2 = 1/3) …”

“…We argue that aldehydes remain influential only under a specific concentration range; otherwise, they may facilitate coke formation and catalyst deactivation. We recommend performing the control and kinetic experiments for a more in-depth understanding, similar to what has recently been reported by the Bhan group on the impact of H 2 and syngas in MTH/MTO catalysis. ,, …”

“…(b) Schematic illustration of the role of syngas in governing the ultimate product selectivity through controlling the equilibrium of olefin-and aromatic-based cycles during MTO catalysis. 185 cocatalytic oxygenate mechanism after simulating FTS reaction conditions (e.g., normal pressure MTH, hydrogenative MTH, and MTH with syngas cofeeding at two different ratios (H 2 / CO = 2/1); see Figure 14). These control experiments are summarized in Figure 14a, where the catalytic trends and results over zeolites ZSM-5 and MOR were typically consistent with the FTS reactions (Figure 11a−d vs Figure 14).…”

“…Section 4.3 and Figure 14b). 185 They reported that CO could mechanistically control the shortest olefin selectivity during MTO reaction via increasing ethylene-to-propylene and ethylene-to-butene ratios only under certain cofeeding conditions (i.e., high CO (3−8 bar) and syngas pressures (24 bar, H 2 /CO ≈ 2−16)). The relative increase in ethylene selectivity during the syngas-cofed MTO reaction was even higher than in the analogous experiments under pure H 2 cofeeding (Figure 14b-I,II).…”