Catalytic Combustion of Dichloromethane over Cr-13X and K-Cr-13X Zeolites Catalysts†

doi:10.7503/cjcu20131076

Abstract

Abstract:

Cr-13X and K-Cr-13X zeolites catalysts with different K and Cr contents were prepared by ion exchange method, and their catalytic performance for catalytic combustion of dichloromethane were evaluated in a conventional fixed bed reactor. Then, these catalysts were characterized via physicochemical techniques. The results showed that, when the Cr content was less than 5.19%, crystallinity of 13X zeolite was not affec-ted by the addition of K and Cr significantly. Cr addition not only enhanced the selectivity of CO₂ product, but also eliminated CH₃Cl by-products. The exchange of K with an appropriate amount enhanced the stability and activity of Cr-13X catalyst, as well as the selectivity of CO₂ and HCl products. The enhancement of the catalytic activity and the products distribution could be accounted for the basis of oxidation and acidity of catalysts. On the condition of gas hourly space velocity of 1×10⁴ h^-1 and dichloromethane concentration of 5692 mg/m³, an optimal 1.31%K-5.01%Cr-13X catalyst was found with t₅₀ at 212 ℃, t₉₈ at 298 ℃ , CO₂ selectivity at 60.6% and HCl selectivity at 96.5%, and this catalyst showed relatively stable catalytic activity during 100 h reaction.

Key words: Dichloromethane, Catalytic combustion, 13X zeolite, Potassium/chromium 13X zeolite

CLC Number:

O643

TrendMD:

ZHANG Lilei, LIU Shaoying, LI Zijian, YAO Jie, WANG Gongying. Catalytic Combustion of Dichloromethane over Cr-13X and K-Cr-13X Zeolites Catalysts^†[J]. Chem. J. Chinese Universities, 2014, 35(4): 812.

Figures/Tables 11

Fig.1 XRD patterns of 13X zeolites series catalysts a. 13X; b. 1.21%Cr-13X; c. 5.19%Cr-13X; d. 1.31%K-5.01%Cr-13X; e. 6.45%Cr-13X.

Table 1 Textural data of 13X zeolites series catalyst

Sample	Surface area, S_BET/(m²·g^-1)	Pore volume, V_p/(cm³·g^-1)	Average pore diameter, D_p/nm
13X	382	0.84	1.0
1.37%Cr-13X	375	0.83	1.0
5.19%Cr-13X	356	0.80	0.9
1.31%K-5.01%Cr-13X	361	0.82	1.0

Table 2 NH3-TPD data of 13X zeolites series catalysts*

Catalyst	Weak acid		Strong acid		Total	Content of total acid/ (μmol·g^-1)
Catalyst	t_m/℃	Content/(μmol·g^-1)			t_m/℃	Content/(μmol·g^-1)
13X	206	227				227
1.37%Cr-13X	211	266				266
5.19%Cr-13X	224	278	477	5	19	297
			551	14
1.31%K-5.01%Cr-13X	218	281	479	5	17	298
			551	12
2.32%K-5.03%Cr-13X	162	224				224

Fig.2 NH3-TPR profiles of 13X zeolites series catalystsa. 13X; b. 1.37%Cr-13X; c. 5.19%Cr-13X; d. 1.31%K-5.01%Cr-13X; e. 2.32%K-5.03%Cr-13X.

Fig.3 H2-TPR profiles of 13X zeolites series catalystsa. 13X; b. 1.37%Cr-13X; c. 2.51%Cr-13X; d. 3.65%Cr-13X; e. 5.19%Cr-13X; f. 1.31%K-5.01%Cr-13X.

Table 3 H2-TPR data of 13X zeolites series catalysts

Catalyst	t_m /℃	H₂ consumption/(μmol· $g cat - 1$ )	Average valence of Cr
1.37%Cr-13X	405	187	4.42
2.51%Cr-13X	408	307	4.27
3.65%Cr-13X	410	425	4.21
5.19%Cr-13X	416	565	4.13
1.31%K-5.01%Cr-13X	401	575	4.19

Table 3 H2-TPR data of 13X zeolites series catalysts

Catalyst	t_m /℃	H₂ consumption/(μmol· $g cat - 1$ )	Average valence of Cr
1.37%Cr-13X	405	187	4.42
2.51%Cr-13X	408	307	4.27
3.65%Cr-13X	410	425	4.21
5.19%Cr-13X	416	565	4.13
1.31%K-5.01%Cr-13X	401	575	4.19

Fig.4 Cr XPS profiles of 5.19%Cr-13X(A, B) and 1.31%K-5.01%Cr-13X(C, D) before(A, C) and after(B, D) stability test

Table 4 XPS results of 5.19%Cr-13X and 1.31%K-5.01%Cr-13X before and after stability test

Catalyst	E_b[Cr(Ⅲ)]/eV		E_b[Cr(Ⅵ)]/eV		Cr surface content(%)	Cr(Ⅲ) content (%)	Cr(Ⅵ) content (%)
Catalyst	2p_3/2	2p_1/2			Cr surface content(%)	2p_3/2	2p_1/2
5.19%Cr-13X	576.8	586.7	579.6	588.6	2.39	63.3	36.7
1.31%K-5.01%Cr-13X	577.8	586.8	580.1	588.7	2.38	60.3	39.7
5.19%Cr-13X(used)	577.4	586.9	579.7	588.8	2.14	62.2	34.8
1.31%K-5.01%Cr-13X(used)	577.7	586.6	579.9	588.7	2.36	61.4	38.6

Fig.5 Relationship between temperature and conversion of DCM combustion over 13X zeolites series catalysts■ 13X; ● 1.37%Cr-13X; ▲ 2.51%Cr-13X; ▼ 3.65Cr-13X; ◆ 5.19%Cr-13X; ? 0.79%K-5.06%Cr-13X; ? 1.31%K-5.01%Cr-13X; ·.32%K-5.03%Cr-13X.

Table 5 Properties of DCM catalytic combustion and products selectivity on t98 temperature of 13X series zeolite catalysts

Catalyst	t₅₀/℃	t₉₀/℃	t₉₈/℃	Selectivity^*(%)
Catalyst	t₅₀/℃	t₉₀/℃	t₉₈/℃	CO₂	CO	HCl	Cl₂	CH₃Cl
13X	283	344	373	7.5	86.1	93.6	0.0	6.4
1.37%Cr-13X	267	338	365	20.3	79.7	97.8	2.2	0.0
2.51%Cr-13X	256	324	363	26.8	73.2	96.2	3.8	0.0
3.65%Cr-13X	234	294	324	48.4	51.6	96.1	3.9	0.0
5.19%Cr-13X	220	276	323	58.9	41.1	95.5	4.5	0.0
0.79%K-5.06%Cr-13X	218	273	320	58.7	42.3	96.2	3.8	0.0
1.31%K-5.01%Cr-13X	212	271	298	60.6	39.4	96.5	3.5	0.0
2.32%K-5.03%Cr-13X	223	278	324	57.8	42.2	97.3	2.7	0.0

Fig.6 DCM combustion stability of 5.19%Cr-13X(a) and 1.31%K-5.01%Cr-13X(b) catalysts

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