It won't be possible if you like to directly download and install the app from your website. There is a different way for enterprise to deploy and install app over the air. Your URL should point to a web service that hosts a manifest plist file in predefined format required by Apple. This service should return the url of manifest file which can then be used as below:
NSString *urlString = // url string where your manifest.plist is deployed on your server.
NSURL *installationURL = [NSURL URLWithString:[NSString stringWithFormat:@"itms-services://?action=download-manifest&url=%@",[urlString stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding]]];
[[UIApplication sharedApplication] openURL];
Hope this answers your question.