Supplementary Information for

A mechanistic basis for the effects of crystallite size on

light olefin selectivity in methanol to hydrocarbons

conversion on MFI

Rachit Khare a, Dean Millar b, and Aditya Bhan a, *

a Department of Chemical Engineering and Materials Science

University of Minnesota - Twin Cities

421 Washington Avenue SE

Minneapolis, Minnesota 55455

USA

b Core R&D

The Dow Chemical Company

1776 Building

Midland, Michigan 48674

USA

* Corresponding author.

E-mail addresses: khare014@umn.edu (R. Khare), dmmillar@dow.com (D. Millar),

abhan@umn.edu (A. Bhan).

S.1. Scanning electron microscopy (SEM) of 500nm-MFI and 2μm-MFI

SEM analysis of 500nm-MFI was performed on a JEOL 6700 field emission gun

scanning electron microscope using lower secondary electron image (LEI) mode at 1.5 kV

accelerating voltage and 8.3 mm working distance. The sample was coated with a layer of

platinum before analysis. The SEM micrographs (Figure S.1 (a) and (b)) show that the crystallite

size of 500nm-MFI sample varies between 200 – 1500 nm. Agglomeration of individual

crystallites is visible and therefore it is difficult to estimate the accurate crystallite size of the

sample. The crystallite size of 500nm-MFI, however, is between that of 40nm-MFI and 2μm-

MFI zeolite samples and is considered to be 500 nm in the calculation of effective crystallite size

of the silylated MFI samples.

SEM analysis of 2μm-MFI was performed on an FEI inspect scanning electron

microscope using the Everhart-Thornley detector (ETD) at 15 kV accelerating voltage and 12.4

mm working distance. The sample was coated with a layer of gold-palladium before the analysis.

Crystallite size of 2μm-MFI was estimated to be 1744 ± 136 nm from the SEM micrograph (see

Figure S.2). A sample-size of 50 particles was used to estimate the crystallite size and Figure S.3

shows a histogram of particle size distribution (very small particles visible in the SEM

micrograph were not considered in crystallite size calculation).

Figure S.1. SEM micrographs of 500nm-MFI.

(a).

(b).

Figure S.2. SEM micrograph of 2μm-MFI.

Figure S.3. Histogram of crystallite size distribution in 2μm-MFI.

1450 1550 1650 1750 1850 1950 2050 2150 225002468

101214161820

Crysatllite size (nm)

Num

ber

of p

artic

eles

S.2. Fourier transform infrared (FT-IR) spectroscopy

The concentration of Brønsted acid sites in the silylated MFI samples as well as the

parent zeolite (500nm-MFI) was determined by Fourier transform infrared (FT-IR) spectroscopy

of adsorbed pyridine. Adsorption of pyridine was performed using a high-temperature Specac IR

transmission cell in conjunction with a Nicolet 6700 FT-IR spectrometer with MCT HighD

detector. Different amount of zeolite samples (10 – 15 mg) were pressed into self-supporting 13

mm diameter wafers using a pellet die and Carver press. Once loaded into the IR cell, samples

were pretreated in 0.75 cm3 s-1 helium flow at 773 K for 1 h. Background spectra were recorded

at 423 K. Multiple 5 µL injections of liquid pyridine were added to the helium flow through a

heat-traced line that passed through the samples until the acid sites were saturated. Samples were

flushed with helium for several minutes to remove any loosely bound pyridine. Spectra were

again recorded at 423 K and now included IR absorption features due to adsorbed pyridine.

Baseline corrected spectra between 2000 – 1350 cm-1 and integrated peak intensities

were obtained using OMNIC software. Due to a measurement error, no data was collected for Si-

MFI-2x. Following the procedure described by Emeis [1] and Zheng et al.,[2] the concentration

of Brønsted acid sites was determined using the peak near 1546 cm -1. To allow quantitative

comparison of the peak intensities, all IR spectra were normalized using the overtone lattice

vibration band of the zeolites near 1850 cm-1. The Brønsted acid site concentration (in mmol g-1)

was calculated using the expression:

CBrønsted = 1.88 (integrated intensity at 1546 cm-1) R2/W;

where CBrønsted is the concentration of Brønsted acid sites (in mmol g-1), R is the radius of catalyst

wafer (6.5 mm), and W is the catalyst weight (in mg).

Table S.1 shows the concentration of Brønsted acid sites as estimated from the FT-IR

spectra of adsorbed pyridine. The results reported are compared to those reported by Zheng et al.

[2] for HZS, HZS-4%, and HZS-3×4% zeolite samples, which correspond to the parent zeolite,

and silylated samples with 4 wt% and 12 wt% SiO2 deposition, respectively.

The concentration of Brønsted acid sites in 500nm-MFI, as determined by FT-IR

spectroscopy of adsorbed pyridine (0.265 mmol g-1), was lower than that calculated from Si/Al

by assuming one Brønsted acid site per Al atom (0.344 mmol g-1). A reason for this may be that

some of the aluminum sites are either inaccessible to pyridine or are in the form of Lewis acid

sites which have an adsorption band (1455 cm-1) distinct from that for the Brønsted acid sites

(1546 cm-1). A monotonic decrease in the concentration of Brønsted acid sites is observed with

increase in SiO2 deposition suggesting that silylation treatment passivated some of the Brønsted

acid sites present near the pore mouth region and on the external surface of the zeolite. Another

reason for this decrease in Brønsted acid site concentration is that some of the aluminum sites

become inaccessible to pyridine due to increased transport limitations with increasing SiO2

deposition.

Table S.1. Concentration of Brønsted acid sites, as determined by FT-IR spectroscopy of adsorbed pyridine at 423 K, in silylated MFI samples and the parent zeolite material. The results are compared to those reported by Zheng et al. in reference [2] .

Zeolitesample

SiO2

deposition(wt%)

CBrønsted

(mmol g-1)Zeolitesamplea

SiO2

deposition(wt%)

CBrønsted

(mmol g-1)

500nm-MFI 0 0.265, 0.344b HZS 0 0.213c, 0.326b

Si-MFI-1x 7 0.229 HZS-4% 4 0.187

SI-MFI-3x 16 0.161 HZS-3×4% 12 0.154

a From Zheng et al. in Reference [2].b From aluminum content assuming one Brønsted acid site per aluminum.c From NH3 adsorption.

S.3. Catalytic reactions of dimethyl ether on MFI

Table S.2. DME space velocity (in mol C [mol Al-s]-1), DME partial pressure (in kPa), net DME conversion (in %, with methanol considered as an unreacted feed), and product selectivity (in %, on a carbon basis) for the reaction of DME over zeolite samples with varying crystallite sizes at 623 K, 57 – 66 kPa DME partial pressure, 46 – 59 % net DME conversion, and 20 min time on stream.

Zeolite sample 2nm- MFI

40nm-MFI

500nm-MFI

2μm-MFI

17μm-MFI

DME space velocity 1.8 2.2 3.2 2.5 0.6

DME partial pressure 66 64 62 61 57

Net DME conversion 59 57 46 47 48

Product selectivity (in %, on a carbon basis):

C2 1.6 5.7 13.2 20.5 20.4

C3 21.0 21.6 21.0 24.2 27.6

C4 16.7 16.4 14.1 15.4 14.6

C5 12.2 11.7 9.6 9.6 8.6

C6 14.1 12.8 10.9 9.0 8.5

C7 11.4 9.5 8.7 6.8 6.5

Methylbenzenes 2.1 5.9 7.4 6.5 5.6

Othersa 21.0 16.4 15.1 7.8 8.2

H/C in Othersb 1.8 1.8 1.8 1.8 1.8

a ‘Others’ fraction includes all C8+ hydrocarbons except polymethylbenzenes.

b The hydrogen to carbon ratio (H/C) in ‘Others’ was calculated based on difference in carbon and hydrogen content of known species in the reaction effluent and converted feed.

Table S.3. DME space velocity (in mol C [mol Al-s]-1), DME partial pressure (in kPa), net DME conversion (in %, with methanol considered as an unreacted feed), and product selectivity (in %, on a carbon basis) for the reaction of DME over silylated MFI samples and the parent zeolite at 623 K, 62 – 64 kPa DME partial pressure, 46 – 58 % net DME conversion, and 20 min time on stream.

Zeolite sample 500nm-MFI Si-MFI-1x Si-MFI-2x Si-MFI-3x

DME space velocity 3.2 3.6 3.3 2.4

DME partial pressure 62 62 64 62

Net DME conversion 46 53 58 53

Product selectivity (in %, on a carbon basis):

C2 13.2 17.9 21.0 22.6

C3 21.0 22.6 24.1 28.0

C4 14.1 14.9 15.5 15.2

C5 9.6 9.9 9.8 8.6

C6 10.9 10.1 9.3 8.1

C7 8.7 7.4 6.2 5.6

Methylbenzenes 7.4 6.9 6.8 5.5

Othersa 15.1 10.3 7.3 6.3

H/C in Othersb 1.8 1.8 1.8 1.8

a ‘Others’ fraction includes all C8+ hydrocarbons except polymethylbenzenes.

b The hydrogen to carbon ratio (H/C) in ‘Others’ was calculated based on difference in carbon and hydrogen content of known species in the reaction effluent and the converted feed.

References

[1] C.A. Emeis, J. Catal. 141 (1993) 347.

[2] S. Zheng, H.R. Heydenrych, A. Jentys, J.A. Lercher, J. Phys. Chem. B 106 (2002) 9552.