Supporting Information

Transcription

1 Supporting Information Confinement Effect and Synergistic Function of H-ZSM-5/Cu-ZnO-Al 2 O 3 Capsule Catalyst for One-Step Controlled Synthesis Guohui Yang, Noritatsu Tsubaki, *,, Jun Shamoto, Yoshiharu Yoneyama, Yi Zhang, Department of Applied Chemistry, School of Engineering, University of Toyama, Gofuku 3190, Toyama , Japan, and JST, CREST, Sanbancho 5, Chiyoda-ku, Tokyo , Japan tsubaki@eng.u-toyama.ac.jp University of Toyama. JST, CREST. S1

2 Experimental The temperature programmed desorption of ammonia (NH 3 -TPD) using a conventional flow apparatus equipped with a thermal conductivity detector (TCD) of gas chromatograph was employed to measure the concentration and intensity of acid sites of bare CZA catalyst, zeolite capsule catalysts CZA-S, CZA- Z and hybrid catalyst CZA-M. The catalyst sample with the amount of 0.1 g was firstly pretreated in flowing helium at 773 K for 2 h, cooled to 400 K, and then to be saturated with NH 3 (20ml/min) for 0.5 h. Samples were subsequently purged with helium gas at 400 K for some time until no NH 3 signal in the effluent could be detected by TCD. Desorption profiles were obtained with the flowing helium (25 ml/min) from 400 K to 900 K at a heating rate of 5 K/min. Result and discussion The NH 3 -TPD profiles of bare CZA catalyst, zeolite capsule catalysts CZA-S, CZA-Z and hybrid catalyst CZA-M were compared in Figure S1. And the quantitative estimation of acid sites was indicated in Table S1. The distribution and strength of acid sites of catalysts can be found on the NH 3 - TPD profiles. The bare CZA catalyst (Figure S1, (a)) exhibited two peaks at the lower temperature of 460 K and 525 K, and one peak at the higher temperature of 840 K. All these peaks should be attributed to the Al 2 O 3 in CZA catalyst. The desorption profiles of hybrid catalyst CZA-M (Figure S1, (d)) showed a slightly higher acidic amount together with a new peak at the temperature of 570 K compared with that of the bare CZA catalyst, due to the addition of H-ZSM-5 zeolite in CZA catalyst. Different from the bare CZA catalyst and hybrid CZA-M catalyst, zeolite capsule catalyst CZA-S (Figure S1, (b)) and CZA-Z (Figure S1, (c)) gave the interesting distribution of acid sites, with a very broad range at the temperature from 460 K to 640 K, which indicated that zeolite capsule catalysts had a significant gradient on the intensity of acidic sites and acidic strength per site. These findings should be ascribed to the aluminum-containing supports used here for constructing the zeolite shell. The aluminum was released and migrated from inner part of bulk of the CZA core catalyst to be transformed into zeolitic Al by hydrothermal synthesis, constructing H-ZSM-5 crystals on core catalyst surface, resulting in the core S2

3 catalyst enwrapped tightly by one layer of zeolite shell. This should be a reason for the higher values of total NH 3 uptake of both zeolite capsule catalysts than those of bare CZA catalyst and CZA-M catalyst, as shown in Table S1. And the formed zeolite shell had a wide distribution on the acidic sites intensity. As clearly demonstrated by NH 3 -TPD in Figure S1, CZA and CZA-M catalyst had similar hightemperature peak at 840 K and similar low-temperature peak at 460 K-525 K, but CZA-M had additional moderate-temperature peak at 570 K, indicating that H-ZSM-5 had moderate strength acidic site. By the hydrothermal synthesis of H-ZSM-5 membrane, a part of Al from the bulk of CZA catalyst core was developed and migrated to zeolite shell, forming new moderate-temperature peak at 640 K, higher than that in CZA-M, indicating more moderate acidic sites of zeolite membrane. It is clear that for CZA-Z having the largest NH 3 uptake, its new moderate-temperature peak at 640 K was larger than that of CZA-S, at the same time, its high-temperature peak at 840 K was also stronger than that of CZA- S, accompanied by its highest acidic site intensity (lowest Si/Al ratio), determining its largest total acidic amount. On the other hand, CZA-S had the smallest high-temperature peak at 840 K, proving that a lot of Al from CZA core bulk moved to zeolite shell to construct acidic site with moderate acidic strength. Considering the lowest acidic site density (highest Si/Al ratio) of CZA-S but its similar total acidic amount to that of CZA-M, the average acidic strength per site, especially for low- or moderatetemperature NH 3 -TPD desorption zone, was rather strong. It can be concluded also that both zeolite capsule catalysts had no formation of hydrocarbons (Others products in Table 1), formed by further dehydration of DME on strong acidic sites, because weak and moderate acidic sites dominated acidic strength distribution of these two catalysts, different with what happened on CZA and CZA-M catalyst where more strong acidic sites existed, leading to formation of hydrocarbons. In more detail, in Figure 3d and Figure 4d of the cross-section EDS line analysis of zeolite capsule catalysts, Si concentration was higher at the zone near outer surface of membrane but Al concentration was almost stable through all thickness points inside membrane, especially for CZA-S. This Si/Al S3

4 gradient distribution inside zeolite membrane informed that Si/Al ratio near the membrane-core interface was low, determining more Al-containing acidic sites near the core, converting methanol to DME quickly and enhancing CO conversion finally by feedback effect. Simultaneously, high Si/Al ratio near the membrane outer surface had low acidic amount, suppressing the undesired side reaction, the further dehydration of DME to hydrocarbons, accomplishing the zero formation of hydrocarbon byproducts via this self-adjusted synergistic effect. (d) Intensity (c) (b) (a) Temperature (K) Figure S1. NH 3 -TPD profiles of (a) CZA, (b) CZA-S, (c) CZA-Z and (d) CZA-M S4

5 Table S1. The NH 3 uptake of bare CZA catalyst, zeolite capsule catalyst CZA-S, CZA-Z, and hybrid catalyst CZA-Z-M Catalyst NH 3 uptake (mmol/g cat.) CZA CZA-S CZA-Z CZA-M S5