The Effect Of Polyethylene Glycol Medium On Structure And Catalytic Performances Of Cuznal Catalysts

The fossil fuels are used effectively and greenly in the21stcentury. At the current technological standard, syngas produced bycoal gasification is used to synthesize ethers, alcohols and otherchemicals, which is a path for the clean and effective usage of coalresources.The concept of green chemistry is put forward and attractedmuch attention. The core of green chemistry is to eliminate thecontamination from the source. Also, the reaction medium has beenattracted more and more attention as a research field.Our group had proposed complete liquid-phase technology whichwas special for slurry reactor. The specialty of this method was thatcatalysts could be heat-treated in liquid paraffin and were turned intoslurry state which could be used directly in the reaction withouttraditional drying and calcination process. Thus, to put green chemistry into reality and expand the application field of complete liquid-phasetechnology, PEG400was used as heat treatment medium and reactionmedium in this paper. The effect of different heat treatment mediums,several molar ratios of CuZnAl and various heat treatmenttemperatures on catalytic performances and catalyst structure wereexplored. Catalysts were characterized by XRD、H2-TPR、NH3-TPD、BET、 XPS、TPO-MS、FTIR、H2-TPD、CO-TPD and so on, theconclusions are made as follows:1. Catalysts prepared by complete liquid-phase technology using liquidparaffin and PEG400as heat treatment mediums and reaction mediumshave different product distribution. The main products are DME andpentane respectively. It is found that the reducibility, phasecomposition, texture properties and acidity have changed significantly.This indicates that liquid mediums play an important role in catalyticperformances and catalyst property.2. After heat treated by PEG400, the size of Cu0crystal grains ofcatalyst has grown bigger. It is deduced that the active site for pentanesynthesis is probably Cu0. The most suitable size for pentane synthesisis21nm which is concluded from catalytic performances and thecharacterization results, indicating the size effect in pentane synthesis.3. Adding Zn species in catalysts can promote the stability of catalystsand adding Al species is beneficial to improve the ability of pentane synthesis, but too much Al content would reduce pentane selectivity.Along with the raising of heat treatment temperature from220℃to280℃, pentane selectivity is not increasing linearly. The mostsuitable temperature for pentane synthesis is260℃.4. Catalyst heat treated by PEG400only has strong acid sites, whilecatalyst heat treated by liquid paraffin has weak and strong acid sites.The types of strong acid sites of two catalysts may be different. Also,the pore sizes of catalysts are bigger after heat treated by PEG400,which is conducive to the proliferation of reaction molecules in thepore canal and promote the synthesis of pentane.5. In this paper, the usage of PEG400broadens the application field ofcomplete liquid-phase technology and enriches catalyst preparationtechnique.