Effect of Activated Carbon Surface Chemistry on the Properties of Cu Particles and the Catalytic Performance for Oxidative Carbonylation of Methanol†

doi:10.7503/cjcu20150995

Abstract

Abstract:

Activated carbon(AC) was thermal treated under nitrogen and ammonia atmosphere, respectively, and used as a support to prepare Cu/AC catalyst by impregnation-calcination method. The influence of AC surface chemistry on the catalyst composition and Cu species particle size as well as the catalytic performace for oxidative carbonylation of methanol has been investigated. AC supports and their corresponding Cu/AC catalysts were characterized intensively by BET, XPS, XRD, H₂-TPR and TEM. The results indicate that the removal of most carboxylic groups by thermal treatment at 600 ℃ under nitrogen atmosphere can improve the Cu species dispersion and reduce the Cu species particle size. However, with further elevating the temperature to 800 ℃, part of lactones, carboxylic anhydrides, phenol and ether groups were removed that lead to the Cu species agglomeration and sintering. Moreover, the decreased AC surface oxygen containing groups has weakened the precursor-support interaction and promoted the reduction of Cu²⁺ to Cu⁺ or Cu⁰. Thermal treatment of AC under ammonia atmosphere results in that more surface oxygen containing groups were removed compared with nitrogen atmosphere. But nitrogen containing groups including pyridinic N(N-6), pyrrole nitrogen(pyrrolic-N) and quaternary nitrogen(N-Q) were introduced at the same time, which was conducive to the Cu species dispersion and reduction of particle size. Besides, the increased surface nitrogen containing groups has enhanced the precursor-support interaction and supressed the reduction of Cu²⁺ to Cu⁺ or Cu⁰. The evaluation result reveals that the catalytic activity of the catalyst varies with the change of the particle size of Cu species. As Cu supported on AC thermal treated at 800 ℃ under ammonia atmosphere, the catalyst shows the optimum catalytic performance, which is ascribed to the smallest Cu species particle size(6.3 nm). The conversion of methanol, space-time yield and selectivity of dimethyl carbonate(DMC) are 9.6%, 278.7 mg·g^-1·h^-1and 68.3%, respectively.

Key words: Surface chemistry, Cu/AC catalyst, Catalyst composition, Particle size, Oxidative carbonylation

CLC Number:

O643

TrendMD:

ZHANG Guoqiang, ZHENG Huayan, HAO Zhiqiang, LI Zhong. Effect of Activated Carbon Surface Chemistry on the Properties of Cu Particles and the Catalytic Performance for Oxidative Carbonylation of Methanol^†[J]. Chem. J. Chinese Universities, 2016, 37(7): 1380.

Figures/Tables 11

Table 1 Textual property of the AC supports and Cu/AC catalysts

Sample	S_BET/(m²·g^-1)	V_P/(cm³·g^-1)	D_P/nm	S_micro/(m²·g^-1)
AC	1597	0.80	2.00	1514
AC-N₂-600	1436	0.71	1.98	1364
AC-N₂-800	1480	0.73	1.98	1407
AC-NH₃-600	1442	0.72	2.01	1376
AC-NH₃-800	1465	0.73	2.00	1389
Cu/AC	1275	0.65	1.98	1190
Cu/AC-N₂-600	1227	0.61	1.98	1163
Cu/AC-N₂-800	1256	0.64	2.00	1184
Cu/AC-NH₃-600	1284	0.64	2.00	1195
Cu/AC-NH₃-800	1293	0.67	1.98	1201

Fig.1 XPS spectra of O1s(A—E) and N1s(A'—E') of the AC supports(A, A') AC-NH3-800; (B, B') AC-NH3-600; (C, C') AC; (D, D') AC-N2-600; (E, E') AC-N2-800.

Table 2 Carbon, oxygen and nitrogen contents of the AC samples obtained by XPS

Sample	Elemental content(mass fraction, %)
Sample	C	O	N
AC	91.1	7.9
AC-N₂-600	94.5	5.5
AC-N₂-800	95.6	4.6
AC-NH₃-600	96.5	2.7	0.8
AC-NH₃-800	97.0	1.6	1.4

Fig.2 Cu2p32 XPS(A—E) and Cu LMM Auger spectra(A'—E') of the Cu/AC catalysts(A, A') AC-NH3-800; (B, B') AC-NH3-600; (C, C') AC; (D, D') AC-N2-600; (E, E') AC-N2-800.

Table 3 Cu2p32 XPS and CuLMM AES curve-fitting analysis of catalysts

Catalyst	E_b of C $u 2 p 32$ /eV		Kinetic energy of CuLMM/eV		Area of C $u a 2 p 32$ (%)		Area of CuLMM^b(%)		C $u + c$ (%)	C $u 0 d$ (%)
Catalyst	Cu²⁺	Cu⁺+Cu⁰	Cu⁺	Cu⁰			Cu²⁺	Cu⁺+Cu⁰	Cu⁺	Cu⁰
Cu/AC-NH₃-800	934.2	932.4	915.5	917.4	63.7	36.3	43.8	56.2	16.0	20.3
Cu/AC-NH₃-600	934.2	932.4	915.5	917.4	57.2	42.8	44.0	56.0	18.8	24.0
Cu/AC	934.2	932.4	915.5	917.2	53.9	46.1	44.4	55.6	20.5	25.6
Cu/AC-N₂-600	934.2	932.4	916.0	918.0	33.3	66.7	65.3	34.7	43.5	23.2
Cu/AC-N₂-800	934.2	932.4	916.0	918.2	21.5	78.5	40.6	59.4	31.8	46.7

Table 3 Cu2p32 XPS and CuLMM AES curve-fitting analysis of catalysts

Catalyst	E_b of C $u 2 p 32$ /eV		Kinetic energy of CuLMM/eV		Area of C $u a 2 p 32$ (%)		Area of CuLMM^b(%)		C $u + c$ (%)	C $u 0 d$ (%)
Catalyst	Cu²⁺	Cu⁺+Cu⁰	Cu⁺	Cu⁰			Cu²⁺	Cu⁺+Cu⁰	Cu⁺	Cu⁰
Cu/AC-NH₃-800	934.2	932.4	915.5	917.4	63.7	36.3	43.8	56.2	16.0	20.3
Cu/AC-NH₃-600	934.2	932.4	915.5	917.4	57.2	42.8	44.0	56.0	18.8	24.0
Cu/AC	934.2	932.4	915.5	917.2	53.9	46.1	44.4	55.6	20.5	25.6
Cu/AC-N₂-600	934.2	932.4	916.0	918.0	33.3	66.7	65.3	34.7	43.5	23.2
Cu/AC-N₂-800	934.2	932.4	916.0	918.2	21.5	78.5	40.6	59.4	31.8	46.7

Fig.3 XRD patterns of the Cu/AC catalystsa. Cu/AC-NH3-800; b. Cu/AC-NH3-600; c. Cu/AC;d. Cu/AC-N2-600; e. Cu/AC-N2-800.

Fig.4 Representative TEM images of the Cu/AC catalysts(A) Cu/AC; (B) Cu/AC-N2-600; (C) Cu/AC-N2-800; (D) Cu/AC-NH3-600; (E) Cu/AC-NH3-800.

Fig.5 Size distribution of the Cu/AC catalysts(A) Cu/AC; (B) Cu/AC-N2-600; (C) Cu/AC-NH3-600; (D) Cu/AC-NH3-800.

Fig.6 H2-TPR profiles of the Cu/AC catalysts(A) Cu/AC-NH3-800; (B) Cu/AC-NH3-600; (C) Cu/AC; (D) Cu/AC-N2-600; (E) Cu/AC-N2-800.

Fig.7 Space time yield(A) and selectivity(B) of the DMC vs. time-on-stream ▼ Cu/AC; ● Cu/AC-NH3-600; ? Cu/AC-NH3-800; ▲ Cu/AC-N2-600; ★ Cu/AC-N2-800.

Fig.8 Dependence of the space time yield of DMC on the Cu particle size

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