Sulfated zirconia support

Zhang, Y. et al. 2007. Investigation of self-humidifying membranes based on sulfonated poly (ether ether ketone) hybrid with sulfated zirconia supported Pt catalyst for fuel cell applications. Journal of Power Sources 168 323-329. 

X-ray dififtaction (XRD) analysis of the freshly calcined catalysts as well as samples used for several hours in the isomerization reaction, only presented the peaks corresponding to the tetragonal form of zirconia. At the same time, for the silica series, XRD confirmed the presence of NiO on the unsulfated catalysts and NiS04 on the sul ted ones. However, XRD did not show any evidence of any of these species for the zirconia series, probably due to their high state of dispersion. Similarly, the XPS data clearly showed the presence of NiO and NiS04 on the unsulfated and sulfated silica-supported catalysts, respectively, but they were not conclusive in the case of zirconia series since both sulfate and oxide species were observed. 

Figure 1. Temperature prograimned reduction of silica- and zirconia-supported catalysts containing nickel and sulfate, a) silica-series b) zirconia-series.

The same behaviour has been found with Cu/ZrOa. A highly dispersed Cu phase was obtained at the surface of zirconla by reacting the support with Cu acetylacetonate [19]. This procedure yields an active catalyst. This catalyst was selective for Na formation at low temperature (< 550 K), but produced only NO2 when the temperature becomes higher than 650 K. However, the same type of catalyst prepared from sulfated zirconia did not produce NO2 but selectively reduces NO to N2 whatever the temperature, with a yield of about 40% at 670 K, and a GHSV of 70000 h l, using only 300 ppm of decane. 

Several other supports have been used in order to generate more-electrophilic Zr systems, including sulfated zirconia [186], sulfated alumina [187], or other sulfated oxide supports [188], though the surface species are quite complex for these sys-... 

Other materials that have been investigated include sulfated zirconia, Br0nsted and Lewis acids promoted on various supports, heteropolyacids, and organic resins, both supported and unsupported. On the whole, these materials also deactivate rapidly, and some of them also exhibit environmental and health hazards. 

Cesium salts of 12-tungstophosphoric acid have been compared to the pure acid and to a sulfated zirconia sample for isobutane/1-butene alkylation at room temperature. The salt was found to be much more active than either the acid or sulfated zirconia (201). Heteropolyacids have also been supported on sulfated zirconia catalysts. The combination was found to be superior to heteropolyacid supported on pure zirconia and on zirconia and other supports that had been treated with a variety of mineral acids (202). Solutions of heteropolyacids (containing phosphorus or silicon) in acetic acid were tested as alkylation catalysts at 323 K by Zhao et al. (203). The system was sensitive to the heteropoly acid/acetic acid ratio and the amount of crystalline water. As observed in the alkylation with conventional liquid acids, a polymer was formed, which enhanced the catalytic activity. 

Moreover, the efficiency of these catalysts could be modihed by tailoring the nature of the metal oxide support and/or reaction conditions (especially the reaction temperature). In this way, interesting conclusions can be obtained when comparing the isobutane/2-butene alkylation catalyzed on two of the most studied catalysts, that is, beta zeolite and sulfated zirconia, when operating at different reaction temperatures. (Table 13.2). ... 

Figure 13.7 shows an effective confrontation between the catalytic results observed on nafion/Si02, sulfated zirconia, and 12-tungstophosphoric acid supported on MCM-41 (HPW/MCM) at a reaction temperature of 50°C. Under these conditions, the HPW/MCM catalyst presents the better yield of TMP. However, similar productivities to that could be obtained on nafion/Si02, or sulfated zirconia, at higher or lower temperatures, respectively, than those optimized for the HPW/MCM-41 catalyst. ... 

Figure 13.7 Conversion of 2-butene and the selectivities to cracking products, TMP, and C9+ hydrocarbons during the isobutane alkylation at 50°C on nafion/Si02 (NS-1), sulfated zirconia (SZ), and MCM-41-supported 12-tungstophosphoric acid (HPW/MCM). Experimental conditions T = 32 C TOS = 1 min molar ratio of 15.

Figure 13.8 Catalyst decay during the isobutane alkylation on nafion/Si02, sulfated zirconia, beta-zeolite, and MCM-41-supported 12-tungstophosphoric acid.

Studies with sulfated zirconia also show similar fast catalyst deactivation in the alkylation of isobutane with butenes. It was found, however, that original activities were easily restored by thermal treatment under air without the loss of selectivity to trimethylpentanes. Promoting metals such as Fe, Mn, and Pt did not have a marked effect on the reaction.362,363 Heteropoly acids supported on various oxides have the same characteristics as sulfated zirconia.364 Wells-Dawson heteropoly acids supported on silica show high selectivity for the formation of trimethylpentanes and can be regenerated with 03 at low temperature (125°C).365... 

Sulfated zirconia catalysts showed selectivities comparable to those of AICI3 in the alkylation of benzene with 1-alkenes to linear alkylbenzenes.396 The mesopor-ous sulfated zirconia sample could be regenerated by solvent extraction or thermal treatment. Phosphotungstic acid supported on sulfated zirconia doped with Fe proved to be very active and highly selective in the alkylation of benzene with propylene at 100-150°C to produce cumene both monoalkylation and cumene formation have better than 90% selectivity.397 It can be regenerated at moderate temperature (350°C). 

Electrophilic chlorination and bromination of methane over supported noble metals9-11 (Pt on A1203, Pd on BaSC ) and solid superacid catalysts9-13 (e.g., TaOF3 on alumina, Nafion-H, zeolites, SbF5-graphite, sulfated zirconia) have been studied (see Section 3.4.2). Monosubstitution with selectivities better than... 

Nitration of o-xylene with N02 has been performed in the gas phase over several zeolites (HBeta, HY, HZSM-5 and HMordenite), as well as on sulfuric acid supported on silica and sulfated zirconia at temperatures between 50 and 130°C.[72] HBeta was found the most active and selective catalyst for the production of 4-o-NX giving ratios of 4-o-NX 3-o-NX as high as 6 1, whereas no dinitro-o-xylene compounds were detected. 

Another important and well studied paramagnetic ion in the lattice of oxide semiconductors is Zr3+ in Zr02. Zirconia dioxide is widely used both as a catalyst of different chemical processes, and as a carrier for constructing supported metal-complex catalysts. In the last years, sulfated zirconia attracted significant interest as an active and selective catalyst in skeletal isomerization of normal alkanes at low temperatures, cracking of paraffins, alkylation and acylation of aromatics [42, 53 and Refs therein]. The appropriate experimental data are collected in the following Table 8.2. 

G. Larsen, E. Lotero, R. D. Parra, L. M. Petkovic, H. S. Silva, and S. Raghavan, Characterization of palladium supported on sulfated zirconia catalysts by DRIFTS, XAS and n - butane isomerzation reaction in the presence of hydrogen, Appl. Catal A 130, 213-226 (1995). 

Friedel-Crafts alkylation processes were traditionally operated at 65-70°C with AICI3 and at 40-60°C with HF. A variety of solid acid catalysts have been developed at the laboratory level, mainly based on zeolites, heteropolyacids or sulfated zirconia (zirconia treated with sulfuric acid). The most recent industrial achievement is the Detal process (UOP-CEPSA) which is based on silica-alumina impregnated with HF. The selectivity towards linear alkylbenzenes exceeds 95%. The cymene processes use AICI3 in the liquid phase or supported phosphoric acid as catalysts. 

Solid acid catalysts play an important role in hydrocarbon conversion reactions in the chemical and petroleum industries [1,2]. Many kinds of solid acids have been found their acidic properties on catalyst surfaces, their catalytic action, and the structure of acid sites have been elucidated for a long time, and those results have been reviewed by Arata [3]. The strong acidity of zirconia-supported sulfate has attracted much attention because of its ability to catalyze many reactions such as cracking, alkylation, and isomerization. Sulfated zirconia incorporating Fe and Mn has been shown to be highly active for butane isomerization, catalyzing the reaction even at room temperature [4]. 

Catalytic activity of bulk and supported sulfated zirconia... 

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